Question 1084537
<pre>
            (liter/hr)   (hours)   (liters)
             RATE        TIME      VOLUME

SMITH         r            35       35r

ALLEN       35-r          20       20(35-r)

Totals       35                       1000
</pre>

r, the unknown rate for the Smith's family; so 35-r is rate for the Allen family.

{{{highlight_green(35r+20(35-r)=1000)}}}

-

{{{35r+700-20r=1000}}}
{{{15r+700=1000}}}
{{{15r=300}}}
{{{highlight(r=20)}}}


Smith family,  20 liters per hour
Allen family,  15 liters per hour