Question

A tap can fill a tank in 15 minutes and another tap can fill in 8 min

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
so ans is d.......

Answer 2

in this topic , another tap have pressure of a water was speed.