A motorist travels from City P to City Q, a distance of 234 km. For the first 78 km, he drives at 52 km/h. For the next 78 km he drives at 39 km/h. For the remaining distance, he drives at x km/h (constant). His overall average speed for the whole trip is 46.8 km/h. What is x?
Show answer & explanation
Correct answer: D
Explanation
Given:
Total distance = 234 km
First distance = 78 km, speed = 52 km/h
Second distance = 78 km, speed = 39 km/h
Remaining distance = speed x km/h
Average speed = 46.8 km/h
Total time = 234 / 46.8 = 5 hours
Time for the first 78 km = 78 / 52 = 1.5 hours
Time for the second 78 km = 78 / 39 = 2 hours
Time so far = 1.5 + 2 = 3.5 hours
Remaining distance = 234 − 156 = 78 km
Remaining time = 5 − 3.5 = 1.5 hours
x = distance / time
x = 78 / 1.5 = 52 km/h