Question 1007975
<pre>
WhichWay    rate       time      distance
O to H      r+w         3        960
H to O      r-w         4        960

{{{system((r+w)*3=960,(r-w)*4=960)}}};
Solve the system.
</pre>

x, volume of the 10% solution
500-x, volume of the 25% solution
{{{(10x+25(500-x))/500=20}}}