Question 1046116
Let {{{ x }}} = ml of pure alcohol to be added
{{{ .25*100 = 25 }}} ml of pure alcohol in the 25% solution
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{{{ ( x + 25 ) / ( x + 100 ) = .7 }}}
{{{ x + 25 = .7*( x + 100 ) }}}
{{{ x + 25 = .7x + 70 }}}
{{{ .3x = 45 }}}
{{{ x = 150 }}}
You need 150 ml of pure alcohol
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check:
{{{ ( x + 25 ) / ( x + 100 ) = .7 }}}
{{{ ( 150 + 25 ) / ( 150 + 100 ) = .7 }}}
{{{ 175 / 250 = .7 }}}
{{{ .7 = .7 }}}
OK