Exercise 2 Page 868

We want to estimate the speed of Marvin's younger brother. Recall that speed is the distance traveled divided by the time spent traveling. Speed = Distance/TimeThe speed and distance in a given time create a direct variation equation. This means that the speed and the distance traveled in a set amount of time are proportional. We know that in the time it takes Marvin to complete 10 loops, his brother completes 8 loops. Therefore, the ratio of distances covered in this time, and also the ratio of their speeds, is 10 8. Distance covered by Marvin/Distance covered by Marvin's brother = 10/8 ⇕ Marvin's speed/Marvin's brother's speed = 10/8 We know that Marvin's speed is 21 miles per hour and we can let Marvin's brother's speed be b. We can substitute these values into our proportion to calculate Marvin's brother's speed.

We have found that Marvin's younger brother's speed is 16.8 miles per hour. Therefore a reasonable estimate for Marvin's brother's speed is between 16 and 17 miles per hour, which corresponds to option H.