Question 661367
Let {{{ x }}} = liters of pure alcohol she must add
{{{ .1*1 = .1 }}} = liters of alcohol in 10% solution
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{{{ ( .1 + x ) / ( 1 + x ) = .25 }}}
{{{ .1 + x = .25*( 1 + x ) }}}
{{{ .1 + x = .25 + .25x }}}
{{{ .75x = .15 }}}
{{{ x = .15/.75 }}}
{{{ x = .2 }}}
She must add .2 liters of pure alcohol
check:
{{{ ( .1 + x ) / ( 1 + x ) = .25 }}}
{{{ ( .1 + .2 ) / ( 1 + .2 ) = .25 }}}
{{{ .3 / 1.2 = .25 }}}
{{{ .3 = .25*1.2 }}}
{{{ .3 = .3 }}}
OK