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Pipes and Cistern - General Aptitude

Q1:

Two pipes can fill a tank in 20 and 24 minutes respectively and a waste pipe can empty 3 gallons per minute. All the three pipes working together can fill the tank in 15 minutes. The capacity of the tank is:

A 60 gallons

B 100 gallons

C 120 gallons

D 180 gallons

ANS:C - 120 gallons

Work done by the waste pipe in 1 minute = 1 - 1 + 1
15 20 24
    = 1 - 11
15 120
    = -  1 .    [-ve sign means emptying]
40
Volume of 1 part = 3 gallons.
40
Volume of whole = (3 x 40) gallons = 120 gallons.