A sink can be filled by the cold water faucet in 6 minutes. The drain can empty a full sink in 9 minutes. If the sink is empty and both the cold water faucet and the drain are open, how long will it take the sink to overflow?
A) 18 minutes
B) 16 minutes
C) 19 minutes
D) 21 minutes
E) 15 minutes

Question

Quizplus · Accepted Answer

The cold water faucet fills the sink at a rate of 1/6 of the sink per minute, and the drain empties it at a rate of 1/9 of the sink per minute. The net rate of filling is 1/6 - 1/9 = 3/18 - 2/18 = 1/18 of the sink per minute. Therefore, it will take 18 minutes to fill the sink.

A Sink Can Be Filled by the Cold Water Faucet