<PRE><B>Question 206806</B>
`Filing a tank. A water tank has an inlet pipe and a drain pipe.
 A full tank came be emptied in 30 minutes if the drain is opened and an empty 
tank can be filled in 45 minutes with the inlet pipe opened. 
If both pipes are accidently opened when the tank is full, then how long will it
 take to empty the tank?
:
Let t = time required to empty the full tank
:
Let the completed job (empty tank) = 1
:
Let filling be minus and draining be plus
:
{{{t/30}}} - {{{t/45}}} = 1
Multiply equation by 90 to get rid of the denominators
3t - 2t = 90
t = 90 minutes to empty the tank
;
:
Check this
{{{90/30}}} - {{{90/45}}} = 
3 - 2 = 1
:
No the tank would not, because more water is leaving than coming in.
Like you leaving the faucet on with drain plug out, unless you have a drain
 problem, the sink will never be filled</PRE>