Q148
ArithmeticTime & Work, Pipes & Cisterns
Two pipes A and B can fill a cistern in 60 minutes and 48 minutes respectively. Both pipes are opened together. The cistern will be filled in half an hour, if the pipe B is turned off after:
- a.6 minutes
- b.18 minutes
- c.20 minutes
- d.24 minutes
Answer: (D) 24 minutes
In 30 minutes A fills $\frac{30}{60} = \frac{1}{2}$ of the cistern, so B must fill the other half. B fills half in $\frac{48}{2} = 24$ minutes, so B is turned off after 24 minutes.