1 Answers

Option 5 : 6 hours

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.

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