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.