An old car is trying to go up and down a hill.
The hill is one mile long on the way up and one mile on the way down.
Going up, the car can average 15 miles per hour.
How fast does the car have to go on the way down to average 30 miles per hour for the entire 2 mile trip?

If you actually do the math on this one, you'll find out it's impossible. To go 30 miles per hour for 2 miles would take you 4 minutes. However, going 15 miles per hour during the 1 mile ascent of the hill also takes 4 minutes, leaving no time left to achieve your 30 mph average. Your old car would need to be going infinitely fast, which, given current technology, is not possible.

Asked by Ben Jenkins · Last updated 3 years ago · 834 views · SOURCE