Adding and subtracting with rational numbers

a) Alex, an eighth grader, and Eric, a seventh grader, need to determine who came
closer to their grade’s state record for the triple jump. Alex jumped 39.75 feet and
Eric jumped 37 feet and 1
1
4
inches. Who was closer to the state record if the
eighth-grade record is 42.25 feet and the seventh-grade record is 39 feet 3
inches? (

1 answer

To determine who was closer to their respective state records, we need to perform the following calculations:

  1. Convert all measurements to the same unit. We'll convert everything to feet.
  • Alex's Jump: 39.75 feet (already in feet)

  • Eric's Jump: \( 37 \text{ feet} \) and \( 1 \frac{1}{4} \text{ inches} \)

    First, convert \( 1 \frac{1}{4} \text{ inches} \) to feet: \[ 1 \frac{1}{4} = \frac{5}{4} \text{ inches} = \frac{5}{4} \div 12 = \frac{5}{48} \text{ feet} \]

    Therefore, Eric's jump in feet is: \[ 37 + \frac{5}{48} = \frac{37 \times 48}{48} + \frac{5}{48} = \frac{1776 + 5}{48} = \frac{1781}{48} \approx 37.52 \text{ feet} \]

  1. Determine the state records in feet as well:
  • Eighth Grade Record: 42.25 feet (already in feet)

  • Seventh Grade Record: \( 39 \text{ feet} \) and \( 3 \text{ inches} \)

    Convert \( 3 \text{ inches} \) to feet: \[ 3 \text{ inches} = \frac{3}{12} = \frac{1}{4} \text{ feet} \]

    Therefore, the seventh-grade record in feet is: \[ 39 + \frac{1}{4} = 39.25 \text{ feet} \]

  1. Calculate the differences between the jumps and the records:
  • Alex's difference from the eighth-grade record: \[ 42.25 - 39.75 = 2.50 \text{ feet} \]

  • Eric's difference from the seventh-grade record: \[ 39.25 - 37.52 \approx 1.73 \text{ feet} \]

  1. Compare the differences:
  • Alex was 2.50 feet away from the eighth-grade record.
  • Eric was approximately 1.73 feet away from the seventh-grade record.

Conclusion: Eric was closer to his state record than Alex was to his.