Question

Three pipes A, B and C can fill a tank in 6 hours. After working at it together for 2 hours, C is closed and A and B can fill the remaining part in 7 hours. The number of hours taken by C alone to fill the cistern is
1. 10
2. 12
3. 14
4. 16

Answer 1

Correct Answer - Option 3 : 14

Total work = 6 unit

The efficiency of A, B and C together = 1 unit

Let efficiency of A and B together be x, then

According to the question

1 × 2 + x × 7 = 6

7x = 6 – 2

x = 4/7

The efficiency of C = Efficiency of A, B and C – Efficiency of A and B

Efficiency of C = 1 – 4/7 = 3/7

C alone can fill the tank in = 6/ (3/7) = 14 hrs