Question

A car can average 15km per hour up a hill to cover 1mile, and it averages 30 km per hr to cover the same hill up and down. What is the average speed of car downhill?

Answer 1

For one mile uphill, average speed is 15kmph. So, time taken is:

1mile/15kmph = 0.107 hrs.

(Since 1 mile = 1.609km)

For one mile uphill + downhill, average speed is 30kmph. So, again:

2mile/30kmph = 0.107 hrs.

What the data is saying is that the car took 0.107 hours to climb up the hill, and then returned back instantly, which is not possible. So, the data given is incorrect. If an answer HAS to be given, the average speed downhill is infinite.