Pipes A and B can fill a tank in 5 and 6 hours respectively. Pipe C can empty it in 12 hours. If all the three pipes are opened together, then the tank will be filled in:
Net part filled in 1 hour = (1/5 + 1/6 - 1/12) = 17/60
∴ Time taken to fill the tank = 1/(17/60) = 60/17 hours
7. Find the wrong term in the series. 2, 54, 300, 1220, 3674, 7350