Multiple choice

Three taps A, B and C together can fill a cistern in 12 hours. All the three taps are opened together for 4 hours and then C is closed. A and B together take 10 hours to fill the remaining part of the cistern. C alone will fill two-third the cistern in?

  1. 48 hours

  2. 50 hours

  3. 60 hours

  4. 40 hours
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let the combined rate of A, B, C be 1/12 cistern per hour. In 4 hours, they fill 4/12 = 1/3 of the cistern, leaving 2/3. A and B together fill 2/3 in 10 hours, so their rate is (2/3)/10 = 1/15 per hour. Therefore, C's rate = 1/12 - 1/15 = 1/60 per hour. To fill 2/3 of the cistern alone, C needs (2/3)/(1/60) = 40 hours.

Keep practicing — related questions