arithmetic - a large tanker can be filled by two pipes a and b in 60 minutes and 40 minutes respectively how many minutes will it take to fill the tanker from empty state if b is used for half the time and a and b fill it together for the other half - skillgun

Part filled by (A + B) in 1 minute = (1/60 + 1/40)
= 1/24.
Suppose the tank is filled in x minutes.
= 4/8.
Then,
=> x/2(1/24 + 1/40) = 1
=> x/2×1/15 = 1
x= 30 min.