Question 941971
Let {{{ x }}} = quarts of pure antifreeze needed
{{{ .1*8 = .8 }}} = quarts of antifreeze in 10% solution
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{{{ ( x + .8 ) / ( x + 8 ) = .2 }}}
{{{ x + .8 = .2*( x +8 ) }}}
{{{ x + .8 = .2x + 1.6 }}}
{{{ .8x = .8 }}}
{{{ x = 1 }}}
1 quart of pure antifreeze is needed
check:
{{{ ( x + .8 ) / ( x + 8 ) = .2 }}}
{{{ ( 1 + .8 ) / ( 1 + 8 ) = .2 }}}
{{{ 1.8 / 9 = .2 }}}
{{{ 1.8 = .2*9 }}}
{{{ 1.8 = 1.8 }}}
OK