Question 536485
Let {{{ x }}} = ml of 70% solution needed
given:
{{{ .7x }}} = ml of copper sulfate in 70% solution
{{{ .25*60 = 15 }}} ml of copper sulfate in 25% solution
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In words:
( final ml of copper sulfate ) / ( final ml of solution ) = 40%
{{{ ( .7x + 15 ) / ( x + 60 ) = .4 }}}
{{{ .7x + 15 = .4*( x + 60 ) }}}
{{{ .7x + 15 = .4x + 24 }}}
{{{ .3x = 24 - 15 }}}
{{{ .3x = 9 }}}
{{{ x = 30 }}}
30 ml of 70% solution are needed
check:
{{{ ( .7*30 + 15 ) / ( 30 + 60 ) = .4 }}}
{{{ ( 21 + 15 ) / 90 = .4 }}}
{{{ 36 = .4*90 }}}
{{{ 36 = 36 }}}
OK