Lesson: Challenging Problem Solving - 22t01

Rates: Average Rates And Combined Rates, Continued

Now solve the following rate problem on your own. Select the correct answer and then click Continue.

A cyclist rides from Foster to Johnston at an average speed of 20 miles per hour and returns immediately along the same route at an average speed of 15 miles per hour. Of the following, which is the closest to the average speed, in miles per hour, for the round trip?

	16.5
	17
	17.5
	18
	18.5

Once again, we can use the average rate formula to solve this problem:

However, we are only given the average speed for each leg of the trip. By picking a number to represent the distances in the trip, we can use the original rate formula to obtain a time for each leg. Let's use 60 to represent the distance of a one-way trip—this number is divisible by 20 and 15, so we can easily find the corresponding time for each leg:

Applying our distance and times to the Average Rate formula, we find:

is closest to Choice (B), 17.

Next to display next topic in the chapter.