Question 1069119
Let {{{ x }}} = ounces of vermouth needed
{{{ .1x }}} = ounces of alcohol in vermouth
{{{ .5*20 }}} = ounces of alcohol in gin
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{{{ ( .1x + .5*20 ) / ( x + 20 ) = .3 }}}
{{{ .1x + 10 = .3*( x + 20 ) }}}
{{{ .1x + 10 = .3x + 6 }}}
{{{ .2x = 4 }}}
{{{ x = 20 }}}
20 ounces of vermouth should be added
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check:
{{{ ( .1x + .5*20 ) / ( x + 20 ) = .3 }}}
{{{ ( .1*20 + .5*20 ) / ( 20 + 20 ) = .3 }}}
{{{ ( 2 + 10 ) / 40 = .3 }}}
{{{ 12 = 12 }}}
OK