-----------------------------------              
|          |volume|percent|solvent|              
-----------------------------------              
|solution 1|      |  0.80 |       |               
-----------------------------------              
|solution 2|  2.0 |  0.30 |       |              
-----------------------------------              
|combined  |      |  0.40 |       |              
-----------------------------------              
solution 1 volume = solution 2 volume X          
        (combined percent - solution 2 percent) /
        (solution 1 percent - combined percent);