Question 766501
An inlet pipe on a swimming pool can be used to fill the pool in 9 hours.
 The drain pipe can be used to drain the pipe in 10 hours.
 If the pool is 2/5 filled and then the inlet pipe and drain pipe are opened,
 how long from that time will it take to fill the pool?
:
Let t = time required to finish filling the pool
:
Let a full pool = 1
The pool is already 2/5 filled, therefore 3/5 remain to filled
:
{{{t/9}}} - {{{t/10}}} = {{{3/5}}}
multiplied eq by 90 to clear the denominators, results:
10t - 9t = 18(3)
t = 54 hrs to fill the pool under these conditions