Question

A bucket is half fulled. a tap can fill the bucket in 8min . another tap can empty the bucket in 16min for the bucket to be completely filled by keeping both the taps open, how much more time will it take?

Answer 1

work done by both taps= 1/15+(-1/8)= -7/120 so tank will be emptied becoz of minus sign.
so time taken= 120/7
given the tank is already half filled
so another half will be emptied in 120/7*1/2
nearly 8 minutes