Question

A car travels 75% of the way from town A to town B by travelling for T hours at an average speed of V mph.
The car travels at an average speed of S mph for the remaining part of the trip. Which of the following
expressions represents the time the car travelled at S mph?

Answer 1

Since the actual distance between A and B doesn’t matter, let’s pick a convenient value to make the arithmetic simpler. Let’s assume A and B are 100 miles apart.

If the car went 75 miles at 50mph, clearly that took 1.5 hours.

If the car went all 100 miles at an average speed of 40mph, clearly the entire trip took 2.5 hours.

Thus it must have taken the car 1 hour to travel the 25 miles remaining, which tells us that S = 25mph.