Question

Pipes P and Q can fill a completely empty tank in 24 minutes and in 36 minutes, respectively, when opened independently. Pipe R can empty the completely filled tank in 30 minutes. Initially all the three pipes P, Q and R, are opened simultaneously. After how many minutes should p ipe Q be closed so that the tank is filled in 1 hour?

Options

• 24

• 18

• 30

• 15

Answer 1

18

Explanation:

Concept : L.C.M = Total capacity of tank

Let is closed after 'x' minutes

A.T.Q, (15 + 10 – 12)x + (15 – 12) × (60 – x) = 360

13x + 180 – 3x = 360

10x = 180

∴ x = 18 min.