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Discussion

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

Answer: C

 

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.

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