Two pipes can fill a tank in 10 and 12 hours respectively while third pipe will make the tank empty in 20 hours. If all three pipes operate simultaneously, in how many hours the tank will be filled ?

2 Answers on this Question

1. In one hour :
   Tank Filled by A = 1/10
   Tank Filled by B = 1/12
   Tank Empty be C = 1/20
   If three pipes are combined then tank filled in one hour =
   1/10 + 1/12 – 1/20
   = 2/15
   2/15 of tanked filled in one hour.
   So time taken to fill tank = 15/2 * 1
   = 7.5 hours

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2. 1/10 + 1/12 -1/20 = 15/2 i.e 7.5 h means 7 h & 30 min

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