sachin_yadav wrote:Hi All,

A car drove from Town A to Town B without stopping. The car traveled the first 40 miles of its journey at an average speed of 25 miles per hour. What was the car's average speed, in miles per hour, for the remaining 120 miles if the car's average speed for the entire trip was 40 miles per hour?

(A) 28
(B) 48
(C) 50
(D) 55
(E) 70

Answer is [spoiler](C)[/spoiler]

The first part (The car traveled the first 40 miles of its journey at an average speed of 25 miles per hour) tells us that the car traveled 40 miles a one speed (25 mph).

This part (for the remaining 120 miles) tells us that the car then traveled 120 more miles at some unknown speed (x mph).

This part (the car's average speed for the entire trip was 40 miles per hour) tells us that the average speed for the entire 160-mile trip was 40mph.

The question asks us to find the average speed during the 120-mile portion of the trip. In other words, find the value of x.

Here's one approach:

If the average speed for the entire 160-mile trip was 40mph, then the trip must taken 4 hours to complete (time = distance/rate = 160/40 = 4hrs)

Now how long did it take to complete the first part of the trip?
Well, during the first part, the car traveled 40 miles at 25 mph
So, the time spent = distance/rate = 40/25 = 8/5 hours

If the entire trip took 4 hours, and the first part took 8/5 hours, then the second part of the trip took 12/5 hours to complete, since 4 - 8/5 = 12/5

Okay, we're almost done.

We know that the second part of the trip took 12/5 hours to complete, and we know that the distance traveled is 120 miles.

Speed = distance/time = 120/(12/5) = 120(5/12) = 50mph

So, the correct answer is C.

Cheers,
Brent