Question 706361
Let {{{ w }}} = mL of water to be added
{{{ .12*20 = 2.4 }}} mL of alcohol in 12% solution
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{{{ 2.4 / ( 20 + w ) = .1 }}}
{{{ 2.4 = .1*( 20 + w ) }}}
{{{ 2.4 = 2 + .1w }}}
{{{ .1w = .4 }}}
{{{ w = 4 }}}
4 mL of water must be added
check:
{{{ 2.4 / ( 20 + 4 ) = .1 }}}
{{{ 2.4 / 24 = .1 }}}
{{{ 2.4 = .1*24 }}}
{{{ 2.4 = 2.4 }}}
OK