Question

Two pipes P and Q can fill a tank in 15 min and 20 min, respectively. Both the pipes are opened together but after 4 min, pipe P is turned off. What is the total time required to fill the tank?

Options

• 15 min 10 sec

• 12 min 20 sec

• 12 min 30 sec

• 14 min 40 sec

Answer 1

14 min 40 sec
Explanation:

Part filled in 4 min = `4(1/15+1/20)=7/5`

Remaining part = `(1-7/15)=8/15`

Part filled by Qin 1 min = `(1/20)`

Therefore, `(1/20):(8/15)::1:x`

⇒ `x=(8/15)xx1xx20=32/3` = 10 min 40 sec.

Therefore, the tank will be full in total (4 min + 10 min 40 sec) = 14 min 40 sec.