Question 1041329
Let {{{ w }}} = ounces of water needed
{{{ .3*15 = 4.5 }}} ounces of alcohol is 30% solution
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{{{ 4.5 / ( w + 15 ) = .25 }}}
{{{ 4.5 = .25*( w + 15 ) }}}
{{{ 4.5 = .25w + 3.75 }}}
{{{ .25w = .75 }}}
{{{ w = 3 }}}
3 ounces of water is needed
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check:
{{{ 4.5 / ( w + 15 ) = .25 }}}
{{{ 4.5 / ( 3 + 15 ) = .25 }}}
{{{ 4.5 = .25*18 }}}
{{{ 4.5 = 4.5 }}} 
OK