# Four pipes P, Q, R and S can fill a cistern in 10, 12.5, 20 and 25 hou

| Four pipes P, Q, R and S can fill a cistern in 10, 12.5, 20 and 25 hours respectively. When will the cistern be full, if first pipe P is opened at 7 am, Q at 8 am, R at 10 am and S at 11 am?

A. 3:09 pm

B. 01:18 pm

C. 12:09 pm

D. 02:15 am

### Right Answer is: C

#### SOLUTION

Let the capacity of cistern be 100.

Then, efficiency of P = 10

Efficiency of Q = 8

Efficiency of R = 5

Efficiency of S = 4

Till 11 am cistern filled by pipe P = 40

Till 11 am cistern filled by pipe Q = 24

Till 11 am cistern filled by pipe R = 5

Cistern filled till 11 am = 69

Now remaining capacity (100 – 69 = 31) of cistern will be filled by Pipes P, Q, R and S together at an efficiency of 27.

Hence, the cistern will be full at 12:09 pm (11 am + 1 hour 9 minutes)

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Four pipes P, Q, R and S can fill a cistern in 10, 12.5, 20 and 25 hou