Question

A hot water tap and a cold water tap fill a bath tub in 12 minutes and 15 minutes respectively.An outlet pipe empties it in 10 minutes. If all three are kept open simultaneously, in how muchtime will the bath tub be full?

Answer 1

for tap 1st

work done in 1 min = 1/12 part of work

for tap 2nf

work done in 1 min = 1/15 part of work

for tap 3rd

work done in 1 min = -1/10 part of work

work done in 1 min together tap = 1/12+1/15-1/10

= (5+4-6)÷60

= (9-6)÷60

= 3÷60

= 1/20 part of work

hence require time for fill tank 20 min