A man travel upstream at 8 miles per hour and downstream 12

A man travel upstream at 8 miles per hour and downstream 12 miles and hour. This took him 2 hours to do. What is his average speed

Solution

The man travels upstream - 8 miles /hour
the man travels downstream - 12 miles
total distance covered = (8+12)=20 miles
total time for travelling this distance - 2 hours
Average speed = total distance/ time
Average speed = 20/2
average speed = 10 miles/hour