1/8 + 1/24 = 1/6
6 * 2 = 12
Pipes A and B can fill a cistern in 8 and 24 minutes respectively. They are opened an alternate minutes. Find how many minutes, the cistern shall be full?

a) 12 min
b) 6 min
c) 4 min
d) 8 min
e) 10 min