A cistern can be filled by taps a,b in 12 hrs and 6 hrs respectively.The full cistern can be emptied by a third tap c in 8 hrs.If all the taps be turned on at the same time, in how much time will the empty cistern be filled completly?
if 24 L tank
Lets us choose to work with a 24 L tank, as the size does not matter.
I choose 24 as 24 = LCF(6,8,12)
tap A adds at 2L per hour
tap B adds at 4L per hour
tap C empties at 3 L per hour.
net effect is 2 + 4 - 3 = add 3 L per hour
hence it will take 24 / 3 = 8 hours