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