Question

Curtis rides his bike 9 miles one way then turns around and rides back. On the return trip, his speed is increased 20% because the wind is at his back. Let s be his speed in miles per hour riding against the wind. What is an expression that represents his total time in hours riding there and back?

Answer 1

The expression that represents his total time is given by "t = 7.5/s" where s is his speed against the wind.

Explanation:

In order to solve this problem we will assign a variable to Curtis speed on the first leg of the trip, this will be called "s". Since the speed on the first part is "s" and the speed on the second part is 20% higher, then the speed on the second part is "1.2s". Each leg of the course is 9 miles long, therefore the time it took to go each way is given by:

time = distance/speed

First part:

t1 = 9/s

Second part:

t2 = 9/1.2s = 7.5/s

The expression for the whole course is the sum of each, so we have:

t = t1 + t2

t = 9/s + 7.5/s

t = (9 + 7.5)/s = (16.5)/s