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Question 1461Question

For centuries, luthiers have attempted to replicate the exquisite sound of violins crafted by Antonio Stradivari in the late seventeenth and early eighteenth centuries. Many researchers believe that the secret lies in the density of the wood, which grew during the Maunder Minimum—a period of abnormally cold European winters. Consequently, recent chemical analyses suggest that Stradivari treated his wood with complex mineral mixtures containing borax, chromium, and table salt to prevent insect infestation.

Which of the following options best replaces the underlined portion of the passage to establish the most logical transition between the two sentences?

Show answer & explanation

Answer: winters; however,

Answer

winters; however,
The correct option correctly identifies the relationship between the two clauses as contrastive (natural climate vs. human chemical intervention) and joins the two independent clauses using proper punctuation (a semicolon followed by the conjunctive adverb and a comma).

Step-by-Step Solution

1
Analyze the relationship between the two independent clauses separated by the transition.
The first clause discusses a natural explanation for the violin's sound (wood density due to cold winters), while the second clause introduces an artificial, chemical explanation (chemical treatments). This represents a contrast.
Identifying the logical connection helps determine the correct transition category.
2
Evaluate the grammar and punctuation required to join two independent clauses.
Both clauses are complete sentences. They must either remain as two separate sentences or be joined by a semicolon or a comma followed by a coordinating conjunction (like 'but'). Joining them with a comma and a conjunctive adverb like 'furthermore' or 'therefore' results in a comma splice.
This rules out options that introduce grammatical errors like comma splices.
3
Select the option that offers both the correct contrast transition and proper punctuation.
The option containing a semicolon and 'however' uses a semicolon to separate the independent clauses and correctly uses 'however' to signal the shift to a contrasting idea.
This is the only grammatically correct option that establishes the appropriate logical relationship.

Key Concept

Sentence-Level Transitions
Estimated Time:1m 0s
Question 1462Question

For all real numbers aa, bb, and cc, let the operation \oplus be defined by ab=ab+1a \oplus b = ab + 1. Which of the following statements must be true?

I. ab=baa \oplus b = b \oplus a
II. a(bc)=(ab)ca \oplus (b \oplus c) = (a \oplus b) \oplus c
III. a(b+c)=(ab)+(ac)a \oplus (b + c) = (a \oplus b) + (a \oplus c)

Show answer & explanation

Answer: I only

Answer

The correct option is the one stating that only Statement I must be true.
The correct option is the one stating that only Statement I must be true. This is because multiplication of real numbers is commutative, making the custom operation commutative. Statement II is false because the operation is not associative, and Statement III is false because the operation does not distribute over addition.

Step-by-Step Solution

1
Evaluate Statement I (ab=baa \oplus b = b \oplus a) by substituting the definition of the operation.
ab=ab+1a \oplus b = ab + 1 and ba=ba+1b \oplus a = ba + 1. Since multiplication of real numbers is commutative, ab=baab = ba, which means ab+1=ba+1ab + 1 = ba + 1. Thus, Statement I is true for all real numbers.
To test the commutative property of the defined operation.
2
Evaluate Statement II (a(bc)=(ab)ca \oplus (b \oplus c) = (a \oplus b) \oplus c) by applying the operation's definition to both sides.
Left side: a(bc)=a(bc+1)=a(bc+1)+1=abc+a+1a \oplus (b \oplus c) = a \oplus (bc + 1) = a(bc + 1) + 1 = abc + a + 1. Right side: (ab)c=(ab+1)c=(ab+1)c+1=abc+c+1(a \oplus b) \oplus c = (ab + 1) \oplus c = (ab + 1)c + 1 = abc + c + 1. Since abc+a+1abc + a + 1 is not equal to abc+c+1abc + c + 1 for all real numbers (for example, if a=1a = 1, b=1b = 1, and c=2c = 2, then 454 \neq 5), Statement II is not always true.
To test the associative property of the defined operation.
3
Evaluate Statement III (a(b+c)=(ab)+(ac)a \oplus (b + c) = (a \oplus b) + (a \oplus c)) using the operation's definition.
Left side: a(b+c)=a(b+c)+1=ab+ac+1a \oplus (b + c) = a(b + c) + 1 = ab + ac + 1. Right side: (ab)+(ac)=(ab+1)+(ac+1)=ab+ac+2(a \oplus b) + (a \oplus c) = (ab + 1) + (ac + 1) = ab + ac + 2. Since ab+ac+1ab+ac+2ab + ac + 1 \neq ab + ac + 2 for all real numbers, Statement III is false.
To test whether the operation distributes over addition.

Key Concept

Identifying properties of operations (commutativity, associativity, and distributivity) on real numbers.

Alternative Method

To quickly disprove Statements II and III, you can substitute simple counterexamples. For Statement II, let a=1,b=1,c=2a=1, b=1, c=2: 1(12)=13=41 \oplus (1 \oplus 2) = 1 \oplus 3 = 4, while (11)2=22=5(1 \oplus 1) \oplus 2 = 2 \oplus 2 = 5. Since 454 \neq 5, Statement II is false. For Statement III, let a=1,b=1,c=1a=1, b=1, c=1: 1(1+1)=12=31 \oplus (1+1) = 1 \oplus 2 = 3, while (11)+(11)=2+2=4(1 \oplus 1) + (1 \oplus 1) = 2 + 2 = 4. Since 343 \neq 4, Statement III is false.
Estimated Time:2m 0s
Question 1463Question

Passage Excerpt:
In 1856, while attempting to synthesize quinine to treat malaria, eighteen-year-old chemist William Henry Perkin accidentally created mauveine, the world’s first synthetic organic dye. At the time, purple clothing was a status symbol affordable only by the extremely wealthy because natural purple dyes were harvested from rare sea snails. [1]

The writer wants to add a sentence at point [1] that contrasts the traditional difficulty of obtaining purple dye with the ease and affordability introduced by Perkin's synthetic alternative. Which choice best accomplishes this goal?

Show answer & explanation

Answer: Unlike the laborious extraction process from snails, Perkin's synthetic method produced a vibrant, inexpensive color that could be easily mass-manufactured.

Answer

Unlike the laborious extraction process from snails, Perkin's synthetic method produced a vibrant, inexpensive color that could be easily mass-manufactured.
The correct option successfully fulfills the rhetorical goal by contrasting the traditional difficulty of obtaining purple dye (the laborious extraction process from snails) with the ease and affordability of Perkin's synthetic alternative (an inexpensive color that could be easily mass-manufactured).

Step-by-Step Solution

1
Analyze the prompt's rhetorical goal.
The target sentence must contrast the traditional difficulty of obtaining purple dye (sea snails) with the ease and affordability of Perkin's synthetic alternative.
This establishes the exact criteria the correct option must meet.
2
Evaluate the choices for grammatical correctness.
The option containing a comma splice is eliminated due to its grammatical error.
ACT English questions require the correct choice to be both grammatically correct and rhetorically appropriate.
3
Evaluate the remaining choices against the rhetorical goal.
Only the option beginning with 'Unlike the laborious extraction...' provides both sides of the contrast requested.
Other grammatically correct options discuss unrelated historical context or subsequent business operations without contrasting the old and new methods.

Key Concept

Meeting Specific Rhetorical Goals
Question 1464Question

Recognized worldwide as a leading authority over volcanic seismology, Dr. Elena Rostova spent decades analyzing tremor patterns before major eruptions. Her research provided crucial warnings that saved thousands of lives.

Which choice best replaces the underlined portion of the sentence?

Show answer & explanation

Answer: authority on

Answer

authority on
The correct choice is the phrase containing 'on' because the idiom 'authority on' is used to denote that someone is an expert in a particular subject or field. In this sentence, the subject is 'volcanic seismology,' making 'authority on' the correct idiomatic phrase.

Step-by-Step Solution

1
Analyze the sentence context to determine the relationship between the noun 'authority' and the field of study 'volcanic seismology'.
The sentence describes Dr. Rostova's high level of expertise in a scientific field, not her power or jurisdiction over a group.
Choosing the correct preposition depends on whether 'authority' refers to power/control or expertise.
2
Evaluate the idiomatic prepositions that pair with 'authority'.
The idiom 'authority on' indicates expertise in a subject, whereas 'authority over' indicates power/control, and 'authority to' indicates permission to act.
This step determines which prepositional collocation is correct for the intended meaning.
3
Select the option that correctly uses the preposition denoting expertise.
The option containing 'authority on' is the correct idiomatic match for the context.
This provides the proper idiomatic correction for the underlined portion.

Key Concept

Idiomatic Preposition Usage with Nouns
Estimated Time:1m 0s
Question 1465Question

The passage below contains a blank indicating a missing punctuation mark. Read the passage and determine which punctuation mark correctly completes the sentence. In the blank provided, what punctuation mark should be placed to ensure the sentence is punctuated correctly?

Fill in the blanks below

Astronomers have long wondered whether other stars in the universe host planets similar to our own. The Kepler space telescope—launched in 2009 to search for Earth-size planets orbiting other starsrevolutionized our understanding of the galaxy by discovering thousands of exoplanets. By monitoring the brightness of over 150,000 stars, Kepler detected the tiny dips in light caused by orbiting planets passing in front of them.
Show answer & explanation

Answer

A dash (—) is the correct punctuation mark to place in the blank.
A dash is correct because it matches the em dash that opens the nonessential parenthetical phrase describing the Kepler space telescope. Under standard English conventions, nonessential elements set off by dashes must be closed with a matching dash to maintain structural consistency.

Step-by-Step Solution

1
Identify the parenthetical, nonessential element in the sentence.
The phrase 'launched in 2009 to search for Earth-size planets orbiting other stars' is a nonessential modifier that provides extra background information about the Kepler space telescope.
Recognizing the syntactic role of the phrase helps determine the punctuation rules that apply to it.
2
Check the punctuation used to introduce the parenthetical element.
The parenthetical element begins with an em dash (—) immediately following the word 'telescope'.
This establishes that the parenthetical phrase is set off by dashes.
3
Apply the rule of punctuation consistency to find the matching mark.
Since the nonessential element is opened with a dash, it must be closed with a matching dash before the main verb 'revolutionized'.
Mismatched punctuation (such as pairing a dash with a comma or parenthesis) is grammatically incorrect on the ACT.

Key Concept

Dash Pair Consistency
Estimated Time:1m 0s
Question 1466Question

The following paragraph contains numbered sentences.

[1] In the early nineteenth century, a Cherokee silversmith named Sequoyah became convinced that written communication was the key to the political and economic power of European settlers. [2] He spent years experimenting with pictographs, but he eventually abandoned this approach as too cumbersome. [3] Instead, he developed a system of 85 symbols, each representing a distinct syllable in the Cherokee language. [4] Within a few years, Cherokee literacy rates soared, even surpassing those of neighboring European settlers.

To make the paragraph most logical, the following sentence should be added:

"This breakthrough allowed speakers of the language to learn to read and write in a matter of weeks, rather than years."

Where is the most logical placement for this sentence?

Show answer & explanation

Answer: after Sentence 3

Answer

after Sentence 3
Placing the sentence after Sentence 3 is correct because 'This breakthrough' refers back to the development of the 85-symbol writing system described in Sentence 3. Additionally, explaining that this system allowed Cherokee speakers to learn reading and writing quickly provides a necessary transition to Sentence 4, which describes the soaring literacy rates.

Step-by-Step Solution

1
Identify the key transition or logical clue in the target sentence.
The target sentence begins with the demonstrative phrase 'This breakthrough,' which requires a clear antecedent describing a successful invention or discovery.
Locating the antecedent for demonstrative adjectives like 'this' or 'these' is the primary way to determine the correct placement of a sentence.
2
Scan the paragraph to locate where a successful breakthrough is described.
Sentence 3 describes the development of a system of 85 symbols, which represents the successful creation of the writing system.
Sentence 1 only introduces Sequoyah's conviction, and Sentence 2 describes a failed attempt, meaning the breakthrough is first established in Sentence 3.
3
Evaluate the flow of placing the sentence after Sentence 3 and before Sentence 4.
The target sentence explains the immediate benefit of the new system (learning in weeks instead of years), which logically sets up the rapid rise in literacy rates mentioned in Sentence 4.
The placement ensures a smooth narrative transition from the development of the system, to its immediate impact, to its long-term societal result.

Key Concept

Sentence Reordering and Placement
Estimated Time:1m 0s
Question 1467Question

In 1856, eighteen-year-old chemist William Henry Perkin was attempting to synthesize quinine, a drug used to treat malaria, in his home laboratory. Instead of quinine, he accidentally produced a dark sludge that, when diluted with alcohol, turned a beautiful shade of purple. Perkin had created mauveine, the first synthetic organic dye, which was an invention that would go on to completely revolutionize the entire global textile industry.

Which of the following options is the most concise and grammatically correct replacement for the underlined portion?

Show answer & explanation

Answer: , which revolutionized the global textile industry

Answer

, which revolutionized the global textile industry
The correct option is both concise and grammatically correct. It avoids the unnecessary words in the original sentence, such as 'was an invention that would go on to' and the redundant modifiers 'completely' and 'entire,' while using active-voice verbs and proper punctuation to attach the relative clause to the main clause.

Step-by-Step Solution

1
Identify wordiness and redundancy in the original underlined portion.
The original phrasing 'was an invention that would go on to completely revolutionize the entire global textile industry' is flagged as wordy. The words 'completely' and 'entire' are redundant because they convey the same meaning.
ACT English questions prioritize conciseness and clarity, so unnecessary or repetitive words must be eliminated.
2
Evaluate the grammar and structure of the remaining options.
The option beginning with a period creates a sentence fragment because relative clauses cannot stand alone. The option using 'it' creates a comma splice because it joins two independent clauses without a conjunction or semicolon.
The correct option must be both concise and grammatically correct.
3
Select the option that is grammatically correct and most concise.
The option ', which revolutionized the global textile industry' is selected as it is active, concise, and correctly punctuated.
This choice successfully removes the wordy phrasing and grammatical errors of the other options.

Key Concept

Eliminating Wordiness
Question 1468Question

Evaluate the four mathematical expressions below and arrange them in order from least to greatest value.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

Expression X, Expression W, Expression Z, Expression Y
Evaluating all four expressions using the proper order of operations (PEMDAS) yields the values: Expression X is 16-16, Expression W is 10-10, Expression Z is 66, and Expression Y is 77. Ordering these values from least to greatest results in the sequence Expression X, Expression W, Expression Z, Expression Y.

Step-by-Step Solution

1
Evaluate Expression X: (3)26×2+5-(-3)^2 - | -6 \times 2 + 5 |
16-16
First, evaluate the exponent: (3)2=9(-3)^2 = 9, which makes the first term 9-9. Next, calculate the expression inside the absolute value bars: 6×2+5=12+5=7-6 \times 2 + 5 = -12 + 5 = -7. The absolute value of 7-7 is 77. Subtracting this value gives 97=16-9 - 7 = -16.
2
Evaluate Expression W: 243(57)2÷(2)-2^4 - 3(5 - 7)^2 \div (-2)
10-10
First, evaluate the exponent: 24=(24)=16-2^4 = -(2^4) = -16. Then, evaluate inside the parentheses: 57=25 - 7 = -2, and square it: (2)2=4(-2)^2 = 4. Next, perform multiplication and division from left to right: 3(4)÷(2)=12÷(2)=6-3(4) \div (-2) = -12 \div (-2) = 6. Adding this to 16-16 gives 16+6=10-16 + 6 = -10.
3
Evaluate Expression Z: 18÷(3)×(2)4+23÷4\frac{-18 \div (-3) \times (-2)}{-4 + 2^3 \div 4}
66
In the numerator, perform multiplication and division from left to right: 18÷(3)=6-18 \div (-3) = 6, and then 6×(2)=126 \times (-2) = -12. In the denominator, evaluate the exponent: 23=82^3 = 8, divide: 8÷4=28 \div 4 = 2, and add: 4+2=2-4 + 2 = -2. Finally, divide the numerator by the denominator: 122=6\frac{-12}{-2} = 6.
4
Evaluate Expression Y: 43×[8(25)2]4 - 3 \times [8 - (2 - 5)^2]
77
Evaluate the innermost parentheses first: 25=32 - 5 = -3, and square it: (3)2=9(-3)^2 = 9. Simplify inside the brackets: 89=18 - 9 = -1. Multiply: 3×(1)=3-3 \times (-1) = 3. Add to the remaining term: 4+3=74 + 3 = 7.
5
Compare the evaluated values to find the correct ordering.
Expression X (16-16) < Expression W (10-10) < Expression Z (66) < Expression Y (77)
Comparing the values 16-16, 10-10, 66, and 77 from least to greatest establishes the correct sequence.

Key Concept

Order of operations dictates evaluating parentheses, exponents, multiplication and division (from left to right), and addition and subtraction (from left to right). Negation outside exponents and absolute values must be treated with care.
Question 1469Question

A writer is editing a draft of an essay about the history of meteorology. Read the passage and answer the question that follows.

[1] In the mid-nineteenth century, meteorology was a fragmented field, relying on isolated observers who recorded local weather conditions without any coordination. [2] British polymath Francis Galton realized that understanding weather patterns required analyzing simultaneous observations across a wide geographical area. [3] In 1861, he distributed standardized recording kits to observers across Europe, asking them to document barometric pressure, wind direction, and temperature at three specific times each day. [4] Galton was also a cousin of Charles Darwin and made significant contributions to the field of statistics. [5] By plotting this synchronized data onto a map using custom-designed symbols, Galton created the first modern weather map, revealing previously invisible atmospheric systems like anticyclones.

The writer is considering deleting Sentence 4 from the passage. Should the sentence be kept or deleted?

Show answer & explanation

Answer: deleted, because it interrupts the focus on Galton's development of the weather map with tangential details about his family and other academic interests.

Answer

deleted, because it interrupts the focus on Galton's development of the weather map with tangential details about his family and other academic interests.
The correct option is the one proposing that the sentence be deleted because it interrupts the paragraph's focus on Galton's development of the weather map. The paragraph details a specific meteorological achievement, and mention of Galton's relation to Charles Darwin or his contributions to statistics is tangential and disrupts the cohesion of the passage.

Step-by-Step Solution

1
Analyze the main focus of the paragraph.
The paragraph describes the fragmented state of early meteorology and details how Francis Galton gathered simultaneous observations to create the first modern weather map.
Understanding the paragraph's core topic is essential for determining whether a sentence is relevant or disruptive.
2
Evaluate the function of Sentence 4 within the paragraph.
Sentence 4 states that Galton was Darwin's cousin and contributed to statistics. These details do not support the main topic of weather map development.
This step determines whether the sentence provides necessary context or acts as a digression.
3
Select the option that correctly recommends deleting the sentence and provides the accurate logical justification.
The sentence should be deleted because it interrupts the main narrative with tangential biographical information.
Identifying the correct action (deletion) and the true rhetorical reason leads to the correct answer.

Key Concept

Sentence Addition and Deletion Decisions
Estimated Time:1m 15s
Question 1470Question

When art restorers began working on the Sistine Chapel ceiling in 1980, they faced the daunting task of reversing centuries of soot accumulation. Over the years, candle smoke, dust, and animal-fat varnishes had obscured Michelangelo's brilliant frescoes under a thick, dark crust. Using a gentle solvent wash, the conservationists painstakingly lifted the grime layer by layer. Critics initially worried that the process would strip away the artist's original detailing. However, the restoration ultimately revealed that Michelangelo had employed a far more vibrant color palette than previously assumed. Rather than the somber, muted tones long associated with the High Renaissance, the frescoes actually boasted brilliant pastels, [1] which were super bright and totally popped in the restored light.

Given the context of the passage, which option most effectively maintains the established tone and style of the narrative?

Show answer & explanation

Answer: that shone with clear intensity

Answer

that shone with clear intensity
The option stating 'that shone with clear intensity' is correct because it maintains the formal, academic, and objective register established in the passage. It describes the vividness of the restored color palette in a way that is concise and stylistically consistent with the narrative.

Step-by-Step Solution

1
Analyze the tone of the surrounding text in the passage.
The passage discusses art history and restoration techniques using a formal, academic, and objective register.
Establishing the target tone allows for the identification and elimination of options that deviate from this register.
2
Evaluate the underlined target phrase for stylistic consistency.
The phrase 'which were super bright and totally popped' is conversational and informal, meaning it must be replaced.
This step determines whether the original text is appropriate or if a change is required.
3
Assess the remaining options for tone register, wordiness, and redundancy.
One option is rejected for being overly pretentious and ornate; another is rejected for repeating synonyms. The option stating 'that shone with clear intensity' is chosen.
This step ensures that the selected option is not only grammatically correct but also concise and tone-consistent.

Key Concept

Stylistic Appropriateness
Estimated Time:1m 0s
Question 1471Question

As a seasoned wildlife tracker, Marcus was highly attuned with the subtle rustles and shifts in the forest undergrowth, often identifying approaching predators long before they came into view.

Which of the following is the most idiomatically correct choice to replace the underlined portion?

Show answer & explanation

Answer: attuned to

Answer

attuned to
The adjective 'attuned' must be paired with the preposition 'to' to idiomatically express being receptive, responsive, or aware. Therefore, the option containing 'attuned to' is correct.

Step-by-Step Solution

1
Identify the word being tested and the preposition that follows it.
The sentence pairs the adjective 'attuned' with the preposition 'with'.
To evaluate if the underlined portion is idiomatically correct or needs replacement.
2
Recall the correct preposition collocation for 'attuned'.
The standard English idiom to mean receptive, responsive, or accustomed to something is 'attuned to'.
Adjectives often require specific prepositions to form correct idiomatic expressions.
3
Select the option that matches this correct idiomatic form.
The option containing 'attuned to' is correct.
This replacement ensures the sentence is idiomatically and grammatically precise.

Key Concept

Idiomatic Preposition Collocation
Estimated Time:45s
Question 1472Question

What is the value of the expression 153×23+1015 - 3 \times 2^3 + 10?

Show answer & explanation

Answer: 11

Answer

The value of the expression is 11.
Evaluating the exponent first gives 23=82^3 = 8. Next, multiplying 3 by 8 yields 24, resulting in the expression 1524+1015 - 24 + 10. Finally, performing addition and subtraction from left to right gives 1524=915 - 24 = -9, and 9+10=1-9 + 10 = 1. Therefore, the value of the expression is 11.

Step-by-Step Solution

1
Evaluate the exponential expression.
23=82^3 = 8
According to the order of operations, exponents must be evaluated before multiplication, division, addition, and subtraction.
2
Perform the multiplication.
3×8=243 \times 8 = 24
Multiplication has higher priority than addition and subtraction.
3
Perform addition and subtraction from left to right.
1524+10=9+10=115 - 24 + 10 = -9 + 10 = 1
Addition and subtraction have equal priority and must be performed in the order they appear from left to right.

Key Concept

Order of Operations (PEMDAS)
Question 1473Question

A writer is editing an essay about inventor Walter Hunt and has drafted the following paragraph:

In 1849, inventor Walter Hunt was twisting a piece of brass wire at his desk, trying to figure out a way to pay off a fifteen-dollar debt. Within three hours, he had designed the first modern safety pin, featuring a clasp that covered the sharp point and a circular loop at the bend to act as a spring. Hunt quickly patented his invention and sold the rights for four hundred dollars, which easily cleared his debt but left him with none of the subsequent millions the product would generate. Over his lifetime, Hunt also designed a sewing machine and a street-sweeping vehicle, though he rarely capitalized on his creations.

The writer is considering adding the following sentence to the paragraph:

'Brass wire was relatively cheap and easy to acquire in nineteenth-century New York.'

Should the writer make this addition?

Show answer & explanation

Answer: No, because it interrupts the narrative flow by introducing a detail about the material's cost that is tangential to Hunt's invention and financial situation.

Answer

No, because it interrupts the narrative flow by introducing a detail about the material's cost that is tangential to Hunt's invention and financial situation.
The correct option correctly identifies that the sentence should not be added. The paragraph's focus is on Walter Hunt's invention of the safety pin and his financial history. The proposed addition about the cost and availability of brass wire introduces a tangential detail that interrupts the flow of the narrative.

Step-by-Step Solution

1
Analyze the paragraph's main idea and focus.
The paragraph focuses on Walter Hunt inventing the safety pin in 1849 to pay a debt, and his general history of not profiting from his inventions.
To evaluate whether a proposed sentence is relevant, we must first establish the central theme and purpose of the existing text.
2
Analyze the proposed sentence for relevance to the main idea.
The proposed sentence discusses the cost and availability of brass wire in nineteenth-century New York.
We need to determine if this new information directly supports or expands upon the established focus of the paragraph.
3
Evaluate the rhetorical impact of adding the proposed sentence.
The sentence introduces a tangential detail about the market availability of brass wire, which shifts focus away from Hunt's personal narrative and financial situation, interrupting the flow of the passage. Therefore, the sentence should not be added.
Comparing the sentence's content to the paragraph's focus helps us make the correct decision and identify the correct rhetorical justification.

Key Concept

Evaluating Relevance for Adding or Deleting Content
Estimated Time:1m 0s
Question 1474Question

Read the following passage and focus on the underlined portion:

Wild yeast and bacteria drive the fermentation of sourdough bread, a process that yields its signature tangy flavor. This natural fermentation is currently slow at this time; however, the long rise allows complex organic acids to develop.

Which of the following options is the most effective and grammatically correct replacement for the underlined portion?

Show answer & explanation

Answer: is slow; however,

Answer

The option that reads 'is slow; however,' is the correct choice because it is concise, eliminates redundancy, and is grammatically correct.
The correct choice is the most concise option that eliminates the redundant phrase 'currently... at this time' and correctly uses a semicolon to separate two independent clauses.

Step-by-Step Solution

1
Identify any redundant elements in the underlined portion of the passage.
The words 'currently' and 'at this time' both mean the same thing, making the phrasing redundant.
ACT English questions require eliminating wordy and repetitive phrasing to achieve maximum conciseness.
2
Evaluate the grammatical structure of the remaining choices to ensure they do not introduce new errors.
The correct option must properly link the two independent clauses. Using a semicolon with 'however' is grammatically correct, whereas using a comma creates a comma splice, and using 'being' creates a fragment.
Eliminating redundancy must not introduce new grammatical errors.

Key Concept

Eliminating Redundancy
Estimated Time:1m 0s
Question 1475Question

Although now cultivated in gardens worldwide, the Ginkgo biloba tree is native of the Zhejiang province in eastern China, where wild stands still survive.

Which choice best replaces the underlined portion of the sentence?

Show answer & explanation

Answer: native to

Answer

native to
The correct option 'native to' uses the standard English idiomatic preposition for describing where a plant or animal species naturally originates. While people can be described as a 'native of' a country, species are described as being 'native to' a region.

Step-by-Step Solution

1
Identify the underlined phrase and determine its grammatical relationship to the surrounding words.
The phrase is 'native of', linking the subject (the Ginkgo biloba tree, a plant species) to its place of origin (Zhejiang province).
This allows us to evaluate whether the preposition 'of' is idiomatically appropriate for a biological species' origin.
2
Recall the idiomatic rules governing the word 'native' and prepositions.
While humans are referred to as 'natives of' a place, plant and animal species are idiomatically described as being 'native to' a geographic area.
This identifies 'native to' as the correct idiomatic match for this context.
3
Evaluate the remaining options for errors.
'native too' is incorrect because it uses the adverb 'too' instead of the preposition 'to'. 'native with' is unidiomatic.
This confirms that 'native to' is the only correct, error-free option.

Key Concept

Idiomatic Preposition Collocations
Estimated Time:45s
Question 1476Question

What is the greatest common factor of 3636 and 5454?

Show answer & explanation

Answer: 18

Answer

The greatest common factor of 3636 and 5454 is 1818.
The greatest common factor of 3636 and 5454 is 1818 because it is the largest integer that divides both numbers evenly (36÷18=236 \div 18 = 2 and 54÷18=354 \div 18 = 3).

Step-by-Step Solution

1
Find the prime factorization of 3636 and 5454.
36=22×3236 = 2^2 \times 3^2 and 54=2×3354 = 2 \times 3^3
Prime factorization decomposes each number into its basic prime building blocks.
2
Identify the common prime factors with their lowest exponents.
The common prime factors are 22 with an exponent of 11 (212^1) and 33 with an exponent of 22 (323^2).
The greatest common factor consists of the product of the lowest powers of the shared prime factors.
3
Multiply the common factors raised to their lowest exponents.
21×32=2×9=182^1 \times 3^2 = 2 \times 9 = 18
Calculating this product gives the greatest common factor.

Key Concept

The greatest common factor (GCF) of two integers is the largest integer that divides both numbers without leaving a remainder. It is calculated by taking the product of the lowest powers of all common prime factors.

Alternative Method

List all factors of both numbers: Factors of 3636 are 1,2,3,4,6,9,12,18,361, 2, 3, 4, 6, 9, 12, 18, 36. Factors of 5454 are 1,2,3,6,9,18,27,541, 2, 3, 6, 9, 18, 27, 54. The largest number present in both lists is 1818.
Estimated Time:45s
Question 1477Question

Ada Lovelace, a nineteenth-century mathematician, is widely celebrated as the world's first computer programmer. Working alongside Charles Babbage, Lovelace wrote notes on his analytical engine that included what is recognized as the first algorithm. While Babbage focused primarily on the mechanical calculations of the machine, Lovelace envisioned its potential to compose music and create art. In her writings, she explained these complex ideas with remarkable clarity, demonstrating a mind that was super smart and totally ahead of its time.

Which choice best maintains the formal, academic tone of the passage?

Show answer & explanation

Answer: intellectually gifted and remarkably forward-thinking

Answer

intellectually gifted and remarkably forward-thinking
The correct option, 'intellectually gifted and remarkably forward-thinking', fits the passage's formal and academic tone perfectly. It conveys the intended meaning clearly, concisely, and with vocabulary appropriate for a historical biography.

Step-by-Step Solution

1
Analyze the context and tone of the passage.
The passage is a historical biography of Ada Lovelace, written in a standard, formal academic tone.
Identifying the established tone helps determine which register of language is appropriate for the underlined section.
2
Evaluate the underlined phrase in relation to the established tone.
The phrase 'super smart and totally ahead of its time' contains slang and informal words that clash with the formal academic tone of the biography.
This shows that the original phrasing is incorrect and must be changed.
3
Evaluate the choices to find the one that maintains the correct tone and is grammatically correct and concise.
The option using 'intellectually gifted and remarkably forward-thinking' is formal, concise, and matches the passage's style. The option with 'perspicacious intellect' is overly pretentious, while the option ending in 'looked ahead to the future' is redundant.
Selecting the option that is formal but not overly pretentious or redundant restores the stylistic appropriateness of the passage.

Key Concept

Stylistic Appropriateness
Question 1478Question

Astronomers have long been fascinated by Saturn’s rings, which are composed of billions of individual ice and rock particles. While early observers believed the rings were solid bands, modern space probes have revealed a highly dynamic system shaped by gravitational interactions with nearby moons. These moons act as "shepherds," clearing gaps in the ring material and maintaining the rings' sharp boundaries. The delicate balance of these structures is super cool to look at, prompting ongoing research into how planetary systems evolve over time.

Which of the following choices best maintains the style and tone of the passage?

Show answer & explanation

Answer: a visually striking phenomenon

Answer

The correct choice is 'a visually striking phenomenon' because it provides a precise, concise, and stylistically appropriate description that aligns with the passage's formal and objective scientific tone.
The correct choice is 'a visually striking phenomenon' because it uses objective, formal, and precise language that matches the scientific tone of the text. It is concise and avoids slang, pretension, and wordiness.

Step-by-Step Solution

1
Analyze the established tone of the passage.
The text utilizes formal, academic, and objective vocabulary suitable for a scientific explanation (e.g., 'composed of billions of individual ice and rock particles', 'dynamic system shaped by gravitational interactions', 'planetary systems evolve over time').
Understanding the surrounding context helps identify the target tone register.
2
Evaluate the underlined phrase in relation to the established tone.
The phrase 'super cool to look at' is colloquial slang, which clashes with the scientific tone.
This confirms that the original phrasing is stylistically inappropriate and must be changed.
3
Assess the remaining options for tone, precision, and conciseness.
The choice 'a visually striking phenomenon' maintains the formal tone without being overly wordy or pretentious. The choice 'an illustrative paradigm of aesthetic grandeur' is too formal and dramatic, while 'something that is extremely beautiful and gorgeous to see' is wordy and redundant.
This identifies the option that restores stylistic consistency without introducing new errors.

Key Concept

Stylistic Appropriateness
Question 1479Question

A red light flashes every 8 seconds, and a blue light flashes every 12 seconds. If they both flash at the same instant, how many seconds will pass before they next flash at the same instant?

Show answer & explanation

Answer: 24

Answer

24 seconds
The correct answer is 24 seconds. To find when both lights will flash at the same time again, we need to find the least common multiple (LCM) of their individual flashing intervals, 8 seconds and 12 seconds. Listing the multiples of each number:
Multiples of 8: 8, 16, 24, 32, 40, 48...
Multiples of 12: 12, 24, 36, 48...
The smallest number that appears in both lists is 24. Thus, the lights will flash together next after 24 seconds.

Step-by-Step Solution

1
Identify the mathematical concept needed to solve the problem.
The problem requires finding the least common multiple (LCM) of the two flashing intervals, 8 and 12.
The lights will next flash together at the smallest positive integer that is a multiple of both 8 and 12.
2
Find the prime factorization of each number.
8=238 = 2^3 and 12=22×312 = 2^2 \times 3.
Prime factorization allows us to construct the LCM by taking the highest power of each prime factor present in either number.
3
Calculate the LCM from the prime factors.
LCM(8,12)=23×3=8×3=24\text{LCM}(8, 12) = 2^3 \times 3 = 8 \times 3 = 24.
We take the highest power of 2, which is 232^3, and the highest power of 3, which is 313^1.

Key Concept

Least Common Multiple
Estimated Time:45s
Question 1480Question

For all non-zero real numbers xx and yy, let the operation \star be defined by xy=xyyxx \star y = \frac{x}{y} - \frac{y}{x}. Which of the following equations must be true for all non-zero real numbers aa, bb, and cc?

Show answer & explanation

Answer: ab=(ba)a \star b = -(b \star a)

Answer

The equation stating that the operation on two numbers is equal to the negative of the operation on those numbers in reverse order, which is ab=(ba)a \star b = -(b \star a)
Applying the definition of the custom operation, the expression for bab \star a is baab\frac{b}{a} - \frac{a}{b}. Factoring out 1-1 from this expression yields (abba)-\left(\frac{a}{b} - \frac{b}{a}\right), which is equivalent to (ab)-(a \star b). Multiplying both sides by 1-1 results in the equation ab=(ba)a \star b = -(b \star a), which must be true for all non-zero real numbers aa and bb.

Step-by-Step Solution

1
Evaluate the expression for bab \star a using the custom operation definition.
ba=baabb \star a = \frac{b}{a} - \frac{a}{b}
To analyze the result of reversing the order of operands.
2
Factor out a negative sign from the right-hand side of the evaluated expression.
ba=(ba+ab)=(abba)b \star a = -\left(-\frac{b}{a} + \frac{a}{b}\right) = -\left(\frac{a}{b} - \frac{b}{a}\right)
To align the expression's terms with the definition of aba \star b.
3
Substitute the definition of aba \star b back into the expression.
ba=(ab)b \star a = -(a \star b)
To establish the relationship between the two permutations of the operation.
4
Negate both sides of the equation to find the equivalent representation.
ab=(ba)a \star b = -(b \star a)
To match the final equation with the options.

Key Concept

Algebraic properties of custom operations and order of operations

Alternative Method

Instead of algebraic proof, substitute small, distinct non-zero integers (e.g., a=2a = 2, b=1b = 1, c=3c = 3) to evaluate the expressions in each option, enabling the elimination of equations that do not hold.
Estimated Time:1m 30s
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