Question 667204
Let {{{ x }}} = gallons of 25% solution needed
{{{ .25x }}} = gallons of chemical in 25% solution
{{{ .5*60 = 30 }}} gallons of  chemical in 50% solution
{{{ (  .25x + 30 ) / ( x + 60 ) = .3 }}}
{{{ .25x + 30 = .3*( x + 60 ) }}}
{{{ .25x + 30 = .3x + 18 }}}
{{{ .05x = 30 - 18 }}}
{{{ .05x = 12 }}}
{{{ x = 240 }}}
240 gallons of the 25% solution must be added
check:
{{{ (  .25x + 30 ) / ( x + 60 ) = .3 }}}
{{{ (  .25*240 + 30 ) / ( 240 + 60 ) = .3 }}}
{{{ ( 60 + 30 ) / 300 = .3 }}}
{{{ 90 / 300 = .3 }}}
{{{ 90 = .3*300 }}}
{{{ 90 = 90 }}}
OK