A full tank has an outlet that empties it in 12 hours and an inlet that fills it in 18 hours. Both are opened. How long does the tank take to empty?

6 hoursCorrect answerYour answer7.2 hoursCorrect answerYour answer30 hoursCorrect answerYour answer36 hoursCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer D

Correct answer: D

Net emptying rate $= \frac{1}{12} - \frac{1}{18} = \frac{3 - 2}{36} = \frac{1}{36}$ .
So 36 hours.

Worth noting

6 hours subtracts the times; the rates subtract.

Ten questions from Boats & Streams, Pipes & Cisterns, at your own pace.

Ten questions from Boats & Streams, Pipes & Cisterns, at your own pace.

Explanation