Question 662306
Let {{{ x }}} = quarts of fluid to be drained
and replaced with pure antifreeze
{{{ .3*5 = 1.5 }}} quarts of antifreeze originally
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{{{ ( 1.5 - .3x + x ) / 5 =  .6 }}}
Note that you started with 5 quarts and
ended with 5 quarts
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{{{ ( 1.5 + .7x ) / 5 = .6 }}}
{{{ 1.5 + .7x = .6*5 }}}
{{{ 1.5 + .7x = 3 }}}
{{{ .7x = 1.5 }}}
{{{ x = 2.14 }}} 
2.14 quarts of fluid should be drained
and replaced with pure antifreeze