Question 1022003
Let {{{ w }}} = gallons of water to be added
{{{ .7*30 = 21 }}} = gallons of antifreeze in 70% solution
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{{{ 21 / ( w + 30 ) = .6 }}}
{{{ 21 = .6*( w + 30 ) }}}
{{{ 21 = .6w + 18 }}}
{{{ .6w = 3 }}}
{{{ w = 5 }}}
5 gallons of water must be added
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check:
{{{ 21 / ( w + 30 ) = .6 }}}
{{{ 21 / ( 5 + 30 ) = .6 }}} 
{{{ 21 / 35 = .6 }}}
{{{ 21 = 21 }}}