Q65
ArithmeticTime & Work, Pipes & Cisterns
Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively. Both the pipes are opened together, but after 4 minutes pipe A is turned off. What is the total time required to fill the tank?
- a.10 min
- b.11 min 45 sec
- c.12 min 30 sec
- d.14 min 40 sec
Answer: (D) 14 min 40 sec
In 4 minutes both pipes fill $4 \times (\frac{1}{15} + \frac{1}{20}) = \frac{7}{15}$ of the tank. B alone fills the remaining $\frac{8}{15}$ in $\frac{8}{15} \times 20 = 10\frac{2}{3}$ minutes, i.e. 10 min 40 sec. Total time = 4 min + 10 min 40 sec = 14 min 40 sec.