- 5 hours
- 6 hours
- 10 hours
- 12 hours

Option 2 : 6 hours

**Given:**

A tank can be filled by two taps A and B in 10 hours and 15 hours respectively

**Calculation:**

According to the question, we have

So, efficiency of (A + B) = 3 + 2 = 5

So, time taken by A + B to fill the tank = (30/5) hours = 6 hours

∴ A and B together can fill the tank in 6 hours.

Pipe A can fill a tank in 10 hours

Tank filled by pipe A in 1 hour = 1/10

Pipe B can fill a tank in 15 hours

Tank filled by pipe B in 1 hour = 1/15** **

Tank filled by them together in 1 hour = 1/10 + 1/15 = 5/30 = 1/6

They can fill the tank in 1/(1/6) = 6 hours

∴ A and B together can fill the tank in 6 hours.

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