A driver covers 60 miles at 30 miles per hour, then another 60 miles at 60 miles per hour. What is the average speed for the whole trip?

Correct answer to question 81 (Arithmetic Reasoning): 40 miles per hour

Method

Average speed is total distance over total time. The legs take 2 hours and 1 hour, so 120 miles in 3 hours gives 40 miles per hour. Averaging 30 and 60 to get 45 ignores that twice as long was spent at the slower speed.