Question 940543
Let {{{ x }}} = ounces of 40% solution to be added
{{{ .4x }}} = ounces of silver nitrate in 40% solution
{{{ .25*12 = 3 }}} = ounces of silver nitrate in 25% silver nitrate solution
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{{{ ( 3 + .4x ) / ( 12 + x ) = .3 }}}
{{{ 3 + .4x = .3*( 12 + x ) }}}
{{{ 3 + .4x = 3.6 + .3x }}}
{{{ .1x = .6 }}}
{{{ x = 6 }}}
6 ounces of the 40% solution should be added
check:
{{{ ( 3 + .4x ) / ( 12 + x ) = .3 }}}
{{{ ( 3 + .4*6 ) / ( 12 + 6 ) = .3 }}}
{{{ 5.4 / 18 = .3 }}}
{{{ 5.4 = 5.4 }}}
OK