Question 793100
L:et {{{ x }}} = liters of mixture to be removed 
and replaced with pure antifreeze
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{{{ .15x }}} = liters of pure antifreeze 
in {{{ x }}} liters of mixture
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{{{ .15*11 = 1.65 }}} liters of pure antifreeze in
original mixture
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Note that you end up with the same number
of liters that you started with
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{{{ ( 1.65 - .15x + x ) / 11 = .25 }}}
{{{ 1.65 + .85x = .25*11 }}}
{{{ .85x = 2.75 - 1.65 }}}
{{{ .85x = 1.1  }}}
{{{ x = 1.294 }}} liters
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check answer:
{{{ ( 1.65 - .15*1.294 + 1.294 ) / 11 = .25 }}}
{{{ ( 1.65 - .194 + 1.294 ) / 11 = .25 }}}
{{{ 2.75 / 11 = .25 }}}
{{{ 2.75 = 2.75 }}}
OK