Exercise 47 Page 352

To find the average speed we can use the relationship between rate — the average speed — distance traveled, and the time needed for the trip. distance=rate* time We can use this equation to express the time needed for the trip in terms of the distance. To do this, let's introduce the variable d for the length of one leg of the journey.

Time Needed to get There

To find the time needed for the forward journey t_(forward), let's use the given rate, 30 miles per hour.

Time Needed to get Back

Using the given rate, we can also find the time needed for Mitsu to get back. Note that the distance back is the same as the distance forward.

Total Time Needed

We can add these times to find the time needed for the round trip journey.

Finding the Average Speed

Notice that the distance of the full journey is 2d, d on the way forward and d on the way back. Now that we know the time needed for the full journey, we can find the rate — the average speed.

Mitsu's average speed for the whole journey is 78019, which is approximately 41.05263 miles per hour. The correct choice is C.