Question 1014082
<pre>
             RATES
Large pipe    1/x
Small pipe    1/(x+4)
Both pipes   1/x+1/(x+4)</pre>


RT=V rule for filling rates and volume.
You can assume the amount of volume to be 1 POOL for this fill rates exercise.



Three hours both pipes, and then 2 hour for just small pipe to finish the 1 pool.
{{{highlight_green((1/x+1/(x+4))3+(1/(x+4))2=1)}}}
Some algebra steps, but just solve for x.