Question

Jill walked 1.5 miles at 3 miles per hour. She then ran 4 miles at 6 miles per hour. Which of the following rates is the closest to Jill’s average rate over the total 5.5 miles?

A. 3.5 miles per hour
B. 3.8 miles per hour
C. 4.2 miles per hour
D. 4.7 miles per hour
E. 5.3 miles per hour

Answer 1

D. 4.7 miles per hour.

Explanation:

Given:

Jill walked 1.5 at the speed =3 miles per hour.

Jill ran 4 miles at the speed =6 miles per hour.

To find:

Average rate over the total 5.5 miles.

Formula used : speed = distance ÷ time

Solution:

Jill walked 3 miles = 1 hour.

Jill walked 1 miles =
`(1)/(3)` hour.

Jill walked 1.5 miles =1.5×
`(1)/(3)` .

Total time for 1.5 miles =0.5 hour.

Jill run 6 miles = 1 hour.

Jill run 1 miles =
`(1)/(6)` hour.

Jill walked 4 miles =4×
`(1)/(6)` .

Total time for 4 miles =0.67 hour

total time for 5.5 miles= 0.5+0.67= 1.17 hour

Speed =distance÷time

Speed= 5.5 miles÷ 1.17 hour

Speed= 4.7 miles per hour

Therefore, the closest average rate over the total 5.5 miles is 4.7 miles per hour.