P drives a car for 5 hours and after every hour he doubles the speed. In the fifth hour, his speed is 128 km/h. What is his average speed of the journey in km/h?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is Option 3 i.e. 49.6.
5th hour speed = 128 → 1st hour = 128 ÷ 16 = 8 km/h
Speeds: 8, 16, 32, 64, 128
Total distance = 8 + 16 + 32 + 64 + 128 = 248 km
Total time = 5 hours
Average speed = = 49.6 km/hr