Correct option is A
Given:
A can fill a tank in 40 min
B can empty the tank in 60 min
Solution:
Convert minutes into efficiency
Take LCM of 40 and 60
LCM (40, 60) = 120
Now, units of time taken by pipe A = => Units = 3
Units of time taken by pipe B = => Units = 2
Time taken by tank to fill the whole tank when both pipes are open = => T = 120 minutes