Question

A tank can be filled by a pipe in 10 minutes and can be emptied by another pipe in 8
minutes. If both pipes are opened when the tank is full, then how long will it take for
the tank to be empty?
A 1 hours
B 1.5 hours
C 30 minutes
D 40 minutes
E 45 minutes

Answer 1

(1/8)-(1/10)= 1/40 = 40 mins