Question 842207
{{{ .3*16 = 4.8 }}} liters of 
antifreeze in radiator initially
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Let {{{ x }}} = liters of mixture to be
removed and replaced with pure antifreeze
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{{{ .3x }}} = liters of pure antifreeze removed
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In words:
( liters of antifreeze you end up with ) / ( liters of mixture you end up with ) = 50%
{{{ ( 4.8 - .3x + x ) / 16 = .5 }}}
{{{ 4.8 + .7x = .5*16 }}}
{{{ .7x = 8 - 4.8 }}}
{{{ .7x = 3.2 }}}
{{{ x = 4.5714 }}} liters should be drained 
and replaced with pure antifreeze
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check answer:
{{{ .3*4.5714 = 1.3714 }}} liters of antifreeze removed
There is now {{{ 4.8 - 1.3714 = 3.4286 }}} liters
of antifreeze in radiator
{{{ x = 4.5714 }}} liters of antifreeze is put back in
There is now {{{ 3.4286 + 4.5714 = 8 }}}  liters of
antifreeze in radiator and total of {{{ 16 }}} liters
{{{ 8/16 = .5 }}} = 50%
OK