Question 1055416
<pre>
PIPE           RATE (TANKSWORTH/HOURS)     TIME       VOLUME

First          1/10                        3&1/2      (1/10)(3&1/2)
Second         1/x
Combined      1/10+1/x                     4          4((1/10)+1/x)
</pre>


Examine the tabulated description for a few minutes.  


First pipe filled some of the tank volume during 3&1/2 hours and then BOTH pipes continued to fill the rest of the tank's volume for 4 hours.  This was filling of the whole 1 tank volume.


{{{(1/10)(3&1/2)+4(1/10+1/x)=1}}}