Question 503890
Let {{{a}}} = gallons of 25% solution needed
given:
{{{ .25a }}} = gallons of alcohol in 25% solution
{{{ .5*20 = 10 }}} gallons of alcohol in 50% solution
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{{{ ( .25a + 10 ) / 30 = .4 }}}
{{{ .25a + 10 = .4*30 }}}
{{{ .25a = 12 - 10 }}}
{{{ .25a = 2 }}}
{{{ a = 8 }}}
8 gallons of 25% solution is needed
check:
{{{ ( .25a + 10 ) / 30 = .4 }}}
{{{ ( .25*8 + 10 ) / 30 = .4 }}}
{{{ 12/30 = .4 }}
{{{ 12 = 12 }}}
OK