Math CentralQuandaries & Queries


Question from Amanda, a student:

Two cars, 142 miles apart, start moving towards each other at the same
time. One is moving 3 times as fast as the other. If they meet 1.7 hrs
later, find the average speed of the slower car in miles per hour?

Hi Amanda,

The distance between the two cars is decreasing. In 1.7 hours it decreases from 142 miles to 0 miles. What is the average speed at which it decreases in miles per hour?

Suppose the speed of the slower car is s miles per hour then the speed of the faster car is 3s miles per hour. Thus the distance between the cars is decreasing at s + 3s = 4s miles per hour.

Solve for s.


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