Worker X can assemble a shed alone in 12 hours, and worker Y can assemble it alone in 6 hours. Working together, how long will it take them?

Correct answer to question 189 (Arithmetic Reasoning): 4 hours

Method

Combine the two rates: X completes 1/12 of the shed per hour and Y completes 1/6, or 2/12, so together they finish 3/12, which is 1/4 of the shed per hour. That means the job takes 4 hours.