Question 96478
Let x=amount of water that must evaporate

Now we know that the amount of pure salt in the original solution (0.04)(32)) has to equal the amount of pure salt in the final solution after evaporation has taken place ((0.06(32-x)).  So our equation to solve is:

0.04(32)=0.06(32-x)  get rid of parens

1.28=1.92-0.06x  subtract 1.92 from both sides

1.28-1.92=1.92-1.92-0.06x  collect like terms

-0.64=-0.06x divide both sides by -0.06

x=10.66667 oz---------------amount of pure water that must evaporate

CK
0.04(32)=0.06(21.33333)

1.28~1.28

Hope this helps----ptaylor