After filling half of a tank with an ingoing pipe that can fill the tank in 8 hours, an outgoing pipe was attached to empty the tank in 10 hours. How much time will it take to fill the whole tank?

Question: After filling half of a tank with an ingoing pipe that can fill the tank in 8 hours, an outgoing pipe was attached to empty the tank in 10 hours. How much time will it take to fill the whole tank?

Solution:
after 4 hours, the tank will be filled in half.
in one hour,
ingoing can fill = 1/8
outgoing can pour = 1/10
total fill-up in one hour = 1/8 - 1/10
= 1/40
∴ to fill te full tank it will take 40 hours.
so, half of the tank will take 20 hours.

total time to fill the tank from the beginning is = 4 + 20 = 24 hours.