Question 891327
Let {{{ x }}} = liters of 10% ethanol mixture to be added
{{{ .6*10 = 6 }}} liters of ethanol in 60% mixture
{{{ ( 6 + .1x ) / ( 10 + x ) = .25 }}}
{{{ 6 + .1x = .25*( 10 + x ) }}}
{{{ 6 + .1x = 2.5 + .25x }}}
{{{ .15x = 3.5 }}}
{{{ x = 23.333 }}}
You should add 23 and 1/3 liters of 10% ethanol mixture
check:
{{{ ( 6 + .1*23.333 ) / ( 10 + 23.333 ) = .25 }}} 
{{{  8.333 / 33.333 = .25 }}}
{{{ 8.333 = .25*33.333 }}}
{{{ 8.333 = 8.333 }}}
OK