Question 779613
{{{ .3*5 = 1.5 }}} quarts of antifreeze in 30% solution
Let {{{ x }}} = quarts of pure antifreeze to be added
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{{{ ( 1.5 + x ) / ( 5 + x ) = .4 }}}
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{{{ 1.5 + x = .4*( 5 + x ) }}}
{{{ 1.5 + x = 2 + .4x }}}
{{{ .6x = 2 - 1.5 }}}
{{{ .6x = .5 }}}
{{{ x = 5/6 }}}
5/6 of a quart of 100% antifreeze must be added
check:
{{{ (( 1.5 + x )) / (( 5 + x )) = .4 }}}
{{{ (( 1.5 + 5/6 )) / (( 5 + 5/6 )) = .4 }}}
{{{ (( 9/6 + 5/6 )) / (( 30/6 + 5/6 )) = .4 }}}
{{{ (( 14/6 )) / (( 35/6 )) = .4 }}}
{{{ 14/35 = .4 }}}
{{{ 2/5  = .4 }}}
{{{ .4 = .4 }}}
OK