Question

A tank has two pipes A and B. Pipe A is for filling the tank and Pipe B is for emptying the tank. Pipe A can fill the tank in 20 hours and Pipe B can empty the tank in 25 hours. How many hours will it take to completely fill a one-fourth empty tank?

• A. 10 hours
• B. 25 hours
• C. 50 hours
• D. 100 hours
• E. 5 hours

Answer 1

The correct option is B

25 hours

In one hour pipe A can fill $\frac{100}{20}$ = 5% of the tank

In one hour pipe B can empty $\frac{100}{25}$ = 4% of the tank

(A+B)'s work = 5-4 = 1%

To fill a one fourth of empty tank, it will take = $\frac{25}{1}$ = 25 hours