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### Question

Pipe A can fill a cistern in 45 minutes, while the pipe B can fill it in 30 minutes. They are alternately open for 1 minute. How long will it take the cistern to fill completely?

**A**

36 mins.

**B**

37 mins.

**C**

35 mins.

**D**

38 mins.

**Soln.**

**Ans: a**

Let the total time taken be 2x minutes. Both X and Y run for x mins. So $(x/30 + x/45)$ = 1. Solving for x, we get x = 18, which gives 2x = 36.