Question 694318
there is {{{ .4*10 = 4 }}} grams of salt in the 40% solution
Let {{{ w }}} = grams of water to be evaporated
When the water is all evaporated, you still have {{{ 4 }}} grams of
salt in the solution
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{{{ 4 / ( 10 - w ) = .5 }}}
{{{ 4 = .5*( 10 - w ) }}}
{{{ 4 = 5 - .5w }}}
{{{ .5w = 5 - 4 }}}
{{{ .5w = 1 }}}
{{{ w = 2 }}}
2 grams of water must be evaporated to
produce a 50% solution
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check:
There is {{{ 10 - 4 = 6 }}} grams of water to start with
There is {{{ 6 - 2 = 4 }}} grams of water left
The solution is {{{ 4 + 4 = 8 }}} grams total
{{{  4 / 8 = .5 }}}
OK