Question

Difficulty: MediumFraction Addition and Subtraction in Context

A parachute rigger is inspecting and cutting suspension line for parachute maintenance. They start with a spool containing 251425 \frac{1}{4} yards of nylon cord. They use 8238 \frac{2}{3} yards to repair a main canopy and 6566 \frac{5}{6} yards to repair a reserve parachute. How many yards of nylon cord remain on the spool?

  1. A
    151215 \frac{1}{2}
  2. B
    147914 \frac{7}{9}
  3. 9349 \frac{3}{4}Answer
  4. D
    101410 \frac{1}{4}

Answer

The correct answer is 9349 \frac{3}{4} yards.
To find the remaining cord, first determine the total amount used by adding 8238 \frac{2}{3} and 6566 \frac{5}{6}. Using a common denominator of 66, this is 846+656=14968 \frac{4}{6} + 6 \frac{5}{6} = 14 \frac{9}{6}, which simplifies to 151215 \frac{1}{2}. Next, subtract this total from the initial amount: 2514−151225 \frac{1}{4} - 15 \frac{1}{2}. Find a common denominator of 44, making it 2514−152425 \frac{1}{4} - 15 \frac{2}{4}. Since 14\frac{1}{4} is smaller than 24\frac{2}{4}, borrow 11 from the 2525 to get 245424 \frac{5}{4}. Finally, 2454−1524=93424 \frac{5}{4} - 15 \frac{2}{4} = 9 \frac{3}{4}.

Step-by-Step Solution

1
Calculate the total amount of nylon cord used for both repairs by finding a common denominator.
823+656=846+656=14968 \frac{2}{3} + 6 \frac{5}{6} = 8 \frac{4}{6} + 6 \frac{5}{6} = 14 \frac{9}{6}
To find the total amount removed from the spool, the two individual parts must be added together using a common denominator of 6.
2
Simplify the total amount used.
1496=1536=151214 \frac{9}{6} = 15 \frac{3}{6} = 15 \frac{1}{2} yards.
Converting the improper fraction part to a mixed number and reducing it to simplest form makes the next calculation easier.
3
Set up the subtraction to find the remaining cord, finding a common denominator for the total length and the used length.
2514−1512=2514−152425 \frac{1}{4} - 15 \frac{1}{2} = 25 \frac{1}{4} - 15 \frac{2}{4}
To find what is left, the used amount must be subtracted from the initial amount on the spool. A common denominator of 4 is required.
4
Regroup the initial mixed number to perform the subtraction.
2454−1524=93424 \frac{5}{4} - 15 \frac{2}{4} = 9 \frac{3}{4} yards.
Since 14\frac{1}{4} is smaller than 24\frac{2}{4}, one whole unit (44\frac{4}{4}) must be borrowed from the whole number 2525 to make the subtraction possible.

Key Concept

Adding and subtracting mixed numbers with unlike denominators, including necessary regrouping (borrowing) from whole numbers.
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