1.  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?
A. 15 min
B. 20 min
C. 27.5 min
D. 30 min

Answer: Option D

Explanation:

Part filled by (A + B) in 1 minute 

 =1+1=1.
604024


Suppose the tank is filled in x minutes.

Then, x 1 + 1 = 1
2 24 40

x x 1 = 1
2 15

x = 30 min.