Question 643971
Let {{{ x }}} = quarts of pure antifreeze needed
{{{ .1*2 = .2 }}} quarts of pure antifreeze in 10% solution
{{{ ( x + .2 ) / ( x + 2 ) = .5 }}}
{{{ x + .2 = .5*( x + 2 ) }}}
{{{ x + .2 = .5x + 1 }}}
{{{ .5x = .8 }}}
{{{ x = 1.6 }}}
1.6 quarts of pure antifreeze must be added
check:
{{{ ( 1.6 + .2 ) / ( 1.6 + 2 ) = .5 }}}
{{{ 1.8 / 3.6 = .5 }}}
{{{ 1.8 = .5*3.6 }}}
{{{ 1.8 = 1.8 }}}
OK