[tex]Formula\ for\ percen\ concentration:\\
Cp=\frac{ms}{mr}*100\%\\\\
ms-mass \ of\ substance\\
mr- mass\ of \ solution\\\\
mr=30 pound\\
ms=x\\
30 \ pounds\ of \ salt-water\ solution-----cp=15\%\\
30 \ pounds\ of \ salt-water\ solution + x\ water --cp=10\%\\ 15\%=\frac{ms}{30}*100\% \\
\frac{15}{100}=\frac{ms}{30}\\
100ms=15*30\ |:100\\
ms=4,5\ pound\\
10\%=\frac{ms}{30+x}*100\%\\
\frac{10}{100}=\frac{4,5}{30+x}\\
10(30+x)4,5*100\\
300+10x=450\\
10x=150\ |:10\\
x=15 pound\\
[/tex][tex]15\ pounds\ of\ water\ must\ be\ added.[/tex]
