- 15
- 20
- 60
- 25

Option 1 : 15

**Given:**

A pipe can fill a tank in 20 mins and another pipe can fill a tank in 30 mins. Pipe A is opened for half of the time and B and A are opened for the other half

**Calculation:**

Part filled by A in 1 min = 1/20

Part filled by B in 1 min = 1/30

Let the time taken to fill the tank be x mins.

According to the question,

{(1/20)(x/2)} + {(1/20 + 1/30)(x/2)} = 1

⇒ x = 15 mins

**∴ The required time is 15 mins.**

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