Two tabs A and B can fill a tank in 10 hours and 15 hours respectively. If both tabs are opened together, the tank will be full in:

6 hours

Time taken by tap A to fill the tank = 10 hours

⇒ Quantity of tank filled by tap A = 1/10 units

Time taken by tap B to fill the tank = 15 hours

⇒ Quantity of tank filled by tap B = 1/15 units

Time taken by A and B together = 1/{(1/10) + (1/15)} = 1/(1/6)

∴ Time taken by A and B together = 6 hrs