Question

Difficulty: MediumSingle Event Probability

A logistics officer is inspecting a shipment of 120120 combat helmets. The shipment contains 4545 large helmets, 3535 medium helmets, 2424 small helmets, and the remaining helmets are extra-large. If the officer randomly selects one helmet for quality control, what is the probability that it is an extra-large helmet? Express your answer as a fraction in simplest form.

Answer: 2/15 / 2 / 15

Answer

2/15
The correct answer is derived by first finding the number of extra-large helmets. Subtracting the known sizes from the total yields 120−104=16120 - 104 = 16 extra-large helmets. The probability of selecting an extra-large helmet is the ratio of extra-large helmets to the total inventory, which is 16120\frac{16}{120}. Simplifying this fraction by dividing both the numerator and the denominator by their greatest common divisor (88) yields the final probability of 215\frac{2}{15}.

Step-by-Step Solution

1
Calculate the total number of known helmets.
45+35+24=10445 + 35 + 24 = 104
To find the number of extra-large helmets, we first need to determine how many helmets belong to the other given size categories.
2
Determine the number of extra-large helmets.
120−104=16120 - 104 = 16
Subtracting the sum of the known sizes from the total number of helmets gives the remaining count, which represents the extra-large helmets.
3
Set up the probability fraction.
16120\frac{16}{120}
The probability of a single event is the number of favorable outcomes (1616 extra-large helmets) divided by the total number of possible outcomes (120120 total helmets).
4
Simplify the fraction.
215\frac{2}{15}
Divide the numerator and denominator by their greatest common divisor, which is 88 (16÷8=216 \div 8 = 2 and 120÷8=15120 \div 8 = 15).

Key Concept

Single Event Probability
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