Question 921722
Let {{{ x }}} = gallons of pure antifreeze to be added
{{{ .4*15 = 6 }}} gallons of antifreeze in 40% mixture
-----------------
{{{ ( x + 6 ) / ( x + 15 ) = .5 }}}
{{{ x + 6 = .5*( x + 15 ) }}}
{{{ x + 6= .5x + 7.5 }}}
{{{ .5x = 1.5 }}}
{{{ x = 3 }}}
3 gallons of pure antifreeze must be added
check:
{{{ ( x + 6 ) / ( x + 15 ) = .5 }}}
{{{ ( 3 + 6 ) / ( 3 + 15 ) = .5 }}}
{{{ 9 / 18 = .5 }}}
{{{ .5 = .5 }}}
OK