Question 697685
{{{ .12*20 = 2.4 }}} kg of pure rubbing alcohol in 12% solution
Let {{{ x }}} = kg of pure rubbing alcohol to be added 
{{{ ( 2.4 + x ) / ( 20 + x ) = .32 }}}
{{{ 2.4 + x = .32*( 20 + x ) }}}
{{{ 2.4 + x = 6.4 + .32x }}}
{{{ .68x = 4 }}}
{{{ x = 5.882 }}}
5.882 kg of pure rubbing alcohol must be added
check answer:
{{{ ( 2.4 + x ) / ( 20 + x ) = .32 }}}
{{{ ( 2.4 + 5.882 ) / ( 20 + 5.882 ) = .32 }}}
{{{ 8.282 / 25.882 = .32 }}}
{{{ 8.282 = .32*25.882 }}}
{{{ 8.282 = 8.282 }}}
OK