Question 892601
Let {{{ x }}} = liters of pure alcohol to be added
{{{ .4*15 = 6 }}} liters of alcohol in 40% solution
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{{{ ( x + 6 ) / ( x + 15 ) = .7 }}}
{{{ x + 6 = .7*( x + 15 ) }}}
{{{ x + 6 = .7x + 10.5 }}}
{{{ .3x = 4.5 }}}
{{{ x = 15 }}}
15 liters of pure alcohol must be added
check:
{{{ ( x + 6 ) / ( x + 15 ) = .7 }}}
{{{ ( 15 + 6 ) / ( 15 + 15 ) = .7 }}}
{{{ 21/30 = .7 }}}
{{{ 21 = .7*30 }}}
{{{ 21 = 21 }}}
OK