Question

Two taps P and Q can fill an empty tank in 15 hours and 30 hours respectively. Both taps were opened at 4 a.m. and after some time, tap Q was closed. It was found that the tank was full at 4 p.m. At what time was the tap Q shut ?

Answer 1

(a) Tank was filled in 12 hours. (P was open for 12 hours).
(b) Tank was filled in 12 hours. P was opened for 12 hours and let Q was opened for x hours.
(c ) `(12)/(15)+(x)/(30)=1`.
`implies (24+x)/(30)=1`
`implies x=6` hours
`:.` Q was opened for 6 hours.