Pump A can fill a tank in 12 minutes, while pump B can fill the same tank in 24 minutes. Both pumps are turned on together to fill the empty tank, but when tank became half full, pump B stops working and rest of the tank is filled by pump A only. How long it took to fill the tank?

10 min

Step-by-step explanation:

Let's say the tank is 24 gallons.

The rate of Pump A is 24 gal / 12 min = 2 gal/min.

The rate of Pump B is 24 gal / 24 min = 1 gal/min.

When both pumps work together, the total rate is 3 gal/min. The time to fill half the tank is:

12 gal / (3 gal/min) = 4 min

The time for Pump A to fill the other half is:

12 gal / (2 gal/min) = 6 min

The total time to fill the tank is 10 min.