<PRE><B>Question 305285</B>
Let {{{x}}} = ounces of water to evaporate
given:
salt in 10% salt solution: {{{.1*90 = 9}}}
In words
(ounces of salt in 10% solution)/(ounces of final solution) = 15%
{{{9/(90 - x) = .15}}}
{{{9 = .15*(90 - x)}}}
{{{9 = 13.5 - .15x}}}
{{{.15x = 13.5 - 9}}}
{{{.15x = 4.5}}}
{{{x = 30}}} ounces
30 ounces of water must be evaporated
check answer:
Removing 30 ounces of water from the {{{90 - 9 = 81}}} ounces
of water leaves {{{51}}} ounces of water
{{{9/(51 + 9) = .15}}}
{{{9/60 = .15}}}
{{{9 = 9}}}
OK
   </PRE>