Pipe A can drain a pool in 10 hours and pipe B can drain it in 15 hours. Working together, how long will the two pipes take to drain the pool?

Correct answer to question 188 (Arithmetic Reasoning): 6 hours

Method

Add the drain rates rather than the times. Pipe A drains 1/10 of the pool per hour and pipe B drains 1/15, and their sum is 1/6 of the pool per hour, so the pool empties in 6 hours.