Question 1163316
<pre>
80% antifreeze solution is 80% alcohol and 20% other stuff.
30% antifreeze solution is 30% alcohol and 70% other stuff.
70% antifreeze solution is 70% alcohol and 30% other stuff.
        
how many| percent | how many  |
gallons | alcohol |  gallons  |
  of    |  as a   |    of     |
solution| decimal |  alcohol  |
--------|---------|-----------|
   x    |   0.8   | 0.8x      |
  70    |   0.3   | 0.3(70)   |  
--------|---------|-----------| 
  x+70  |   0.7   | 0.7(x+70) |

The equation comes from the last column

0.8x + 0.3(70) = 0.7(x+70)

Solve that.  The answer is more than 200 and less than 300 gallons.

That's a big answer, but we should expect that because 30% is pretty 
weak compared to 70%, so it should take a lot.

Edwin</pre>