Question 836239
A tank is filled in 9hrs and drained in 11hrs.
 How long will it take to fill the tank if the drain is left half open?
:
Assuming a half open drain will drain the tank in 22 hrs
Let t = time required to fill the tank if both fill and half-drain pipe are open
Let the full tank = 1
:
{{{t/9}}} - {{{t/22}}} = 1
multiply by 198 to clear the denominators
22t - 9t = 198
13t = 198
t = 198/13
t = 15.23 hrs to fill the tank with drain half open