Two pipes, A and B, can fill the tank in 60 hours and 90 hours, respectively. If both the pipes are opened simultaneously, in how many hours will 75% of the tank be filled?

Given:

Pipe A fills the tank in 60 hours

Pipe B fills the tank in 90 hours

We need to find the time taken to fill 75% of the tank when both pipes are opened together.

Calculation:

Assume LCM of 60 and 90 as total capacity of tank = 180 units

Work done by Pipe A in 1 hour = 180 ÷ 60 = 3 units

Work done by Pipe B in 1 hour = 180 ÷ 90 = 2 units

Combined work in 1 hour = 3 + 2 = 5 units

75% of 180 units = (75/100) × 180 = 135 units

Time required = Total work / Work per hour

Time = 135 ÷ 5 = 27 hours

∴ The tank will be 75% filled in 27 hours