[tex]64 \times 2\%=64 \times 0.02=1.28[/tex]
64 ounces of a 2% salt solution contains 1.28 ounces of salt and thus 62.72 ounces of water.
The mass of the 10% solution is (x+1.28), where x is the mass of water.
1.28 divided by (x+1.28) must be equal to 10%.
[tex]\frac{1.28}{x+1.28} \times 100\%=10\% \\
\frac{1.28}{x+1.28} \times 100=10 \\
1.28 \times 100=10(x+1.28) \\
128=10x+12.8 \\
115.2=10x \\
x=11.52[/tex]
The 10% solution contains 11.52 ounces of water.
[tex]62.72-11.52=51.2[/tex]
51.2 ounces of water must be evaporated.
