Question 487016
Let {{{ x }}} =  gallons of a 60% antifreeze solution needed
{{{ .6x }}} = gallons of antifreeze in the 60% solution
{{{ .25*60 = 15 }}} = gallons of antifreeze in 25% solution
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In words:
( total gallons of antifreeze ) / ( total gallons of solution ) = 50%
{{{ ( .6x + 15 ) / ( 60 + x ) = .5 }}}
{{{ .6x + 15 = .5*( 60 + x ) }}}
{{{ .6x + 15 = 30 + .5x }}}
{{{ .1x = 30 - 15 }}}
{{{ .1x = 15 }}}
{{{ x = 150 }}}
150 gallons of 60% antifreeze solution must be added
check answer:
{{{ ( .6x + 15 ) / ( 60 + x ) = .5 }}}
{{{ ( .6*150 + 15 ) / ( 60 + 150 ) = .5 }}} 
{{{ ( 90 + 15 ) / 210 = .5 }}}
{{{ 105/210 = .5 }}}
{{{ 105 = 105 }}}
OK