Two pipes X and Y can fill a tank in 14 hours and 21 hours, respectively. Both pipes are opened simultaneously to fill the
tank. In how many hours will the empty tank be filled?

Question

Accepted Answer

Pipe X fills the tank in 14 hours, so its rate is 1/14 tank per hour.

Pipe Y fills the tank in 21 hours, so its rate is 1/21 tank per hour.

When both pipes are opened together, their combined rate is (1/14 + 1/21) tanks per hour.

To add these, find the common denominator:  
1/14 = 3/42 and 1/21 = 2/42

Combined rate = (3/42 + 2/42) = 5/42 tanks per hour.

Time taken to fill the tank together = 1 / (5/42) = 42/5 = 8.4 hours.

Convert 8.4 hours to mixed fraction:  
8.4 = 8 + 0.4 = 8 + 2/5 = 8 2/5 hours.

The correct answer is 8 2/5 hours, which corresponds to option 1.

Therefore, option 1 is correct.

Answer

Answer

Answer