IBPS SO Prelims Exam Model Paper 10

Given:
Pipe P's 1 hour's work = 1/18
Pipe Q's 1 hour's work = 1/12
Calculation:
Pipe (P + Q)’s 1 hour's work = 1/18 + 1/12 = 5/36
Pipe (P + Q)’s 7 hours work = 7 × 5/36 = 35/36
⇒ Remaining work = 1 – 35/36 = 1/36
Then,
⇒ 1/36 × R = 1
⇒ R = 36
Pipe R's 1 hour's work = 1/36
⇒ Pipe (P + Q + R)’s 1 hour's work = 1/18 + 1/12 + 1/36 = 1/6
∴ It will take 6 hours to fill the tank when all three pipes are opened simultaneously.