Pipes and Cisterns Practice Test 1 with solutions

Work done by A and B together in one minute
= $\frac{1}{60}+\frac{1}{40}$
= $\frac{2+3}{120}$ = $\frac{5}{120}$
= $\frac{1}{24}$
So, tank was scheduled to be filled in 24 minutes
⇒ Pipe B burst after 20 minutes.
So, part of tank filled in 20 minutes by A and B = 20 × $\frac{5}{120}$ = $\frac{5}{6}$
Part of tank that remains empty = $\frac{1}{6}$
Time taken by Pipe A to fill the tank = 60 minutes
Time taken by A to fill $\frac{1}{6}$ th part of the tank = $60\times \frac{1}{6}$ = 10 minutes
Total time taken to fill the tank = 20 + 10 = 30 minutes.