Advertisement

### Question

Pipe A can fill a cistern in 30 minutes, while the pipe B can fill it in 20 minutes. They are alternately open for 1 minute. How long will it take the cistern to fill completely?

**A**

24 mins.

**B**

25 mins.

**C**

23 mins.

**D**

26 mins.

**Soln.**

**Ans: a**

Let the total time taken be 2x minutes. Both X and Y run for x mins. So $(x/20 + x/30)$ = 1. Solving for x, we get x = 12, which gives 2x = 24.