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

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

A. 10 min 20 sec

B. 11 min 45 sec

C. 12 min 30 sec

**D. 14 min 40 sec (Correct)**

Explanation:

Part filled in 4 minutes = 4(1/15 + 1/20) = 7/15

Remaining part = 1 – 7/15 = 8/15

Part filled by B in 1 minute = 1/20

1/20 : 8/15 :: 1 ; x

x = 8/15 * 1 * 20 = 10 2/3 min = 10 min 40 sec.

The tank will be full in (4 min. + 10 min. 40 sec) = 14 min 40 sec.