Pump A can fill a tank in 6 hours and pump B can fill the same tank in 3 hours. Working together, how long will they take to fill it?

Correct answer to question 14 (Arithmetic Reasoning): 2 hours

Method

Add the rates, not the times. Pump A fills 1/6 of the tank per hour and pump B fills 1/3, so together they fill 1/6 + 2/6 = 1/2 of the tank each hour. Filling the whole tank therefore takes 2 hours.