Question 760829
Let {{{ x }}} = gallons of pure alcohol to be added
{{{ .2*50 = 10 }}} = gallons of pure alcohol in 20% mixture
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{{{ ( 10 + x ) / ( 50 + x ) = .5 }}}
{{{ 10 + x = .5*( 50 + x ) }}}
{{{ 10 + x = 25 + .5x }}}
{{{ .5x = 15 }}}
{{{ x = 30 }}}
30 gallons of pure alcohol needs to be added
check:
{{{ ( 10 + x ) / ( 50 + x ) = .5 }}}
{{{ ( 10 + 30 ) / ( 50 + 30 ) = .5 }}}
{{{ 40/80 = .5 }}}
{{{ 40 = .5*80 }}}
{{{ 40 = 40 }}}
OK