Question

Tap A fills a tank in 12 hours, while Tap B empties the same tank in 20 hours. If both the taps are open together, the tank will fill in:
1. 36 hours 24 min
2. 24 hours 45 min
3. 20 hours
4. 30 hours

Answer 1

Correct Answer - Option 4 : 30 hours

Given:

A fills a tank in 12 hours

B empties the same tank in 20 hours

Both taps are open together.

Concept used:

Total days = (total work)/efficiency

Explanation:

LCM of 12 and 20 is 60 

Let the total capacity of the tank be = 60 litre

Efficiency of A = + 5 liter/hour

Efficiency of B = - 3 liter/hour

Both A + B can fill the tank in 60/(5 - 3) hours.

⇒ 60/2 = 30 hours

∴ The tank will fill in 30 hours.