Question 947477
Let {{{ x }}} = cm3 of pure alcohol to be added
{{{ .6*10 = 6 }}} cm3 of pure alcohol in 60% solution
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{{{ ( x + 6 ) / ( x + 10 ) = .9 }}}
{{{ x + 6 = .9*( x + 10 ) }}}
{{{ x + 6 = .9x + 9 }}}
{{{ .1x = 3 }}}
{{{ x = 30 }}}
30 cm3 of pure alcohol should be added
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check:
{{{ ( x + 6 ) / ( x + 10 ) = .9 }}}
{{{ ( 30 + 6 ) / ( 30 + 10 ) = .9 }}}
{{{ 36 / 40 = .9 }}}
{{{ 36 = .9*40 }}}
{{{ 36 = 36 }}}
OK