Question

# Q1. Pipe A can fill a tank in 10 minutes. Pipe B can fill the same tank in 15 minutes. Pipe C at the bottom of the tank is a waste pipe for emptying the tank. After opening Pipe A and Pipe B, a man returns when the tank should have been full. However, he finds that Pipe C was also kept open and shuts it and the tank overflows in the next 2 minutes. How many minutes will Pipe C take to empty the tank if Pipes A and B are kept shut?

CAT 2021

Correct option is

**Explanatory Answer :**

Pipe A and Pipe B together fill 1/10+1/15=5/30=1/6th of the tank in a minute

so, the man would have returned to the tank 6 minutes after opening the taps hoping to see the tank full. However, he finds Pipe C open and shuts it immediately.

After shutting Pipe C, the tank was full in 2 minutes.

Therefore, in the last two minutes 1/6×2=1/3rd of the tank would have been filled by Pipe A and Pipe B.

This is the quantum of water that Pipe C would have drained during the first 6 minutes.

lf Pipe C drained 1/3rd of the tank in 6 minutes, then it will take 18 minutes to drain the entire tank.