Question 555010
let {{{ x }}} = ml of pure acid needed
{{{ .25*500 = 125 }}} ml of pure acid in 25% solution
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{{{ ( x + 125 ) / ( x + 500 ) = .75 }}}
{{{ x + 125 = .75*( x + 500 ) }}}
{{{ x + 125 = .75x + 375 }}}
{{{ .25x = 375 - 125 }}}
{{{ .25x = 250 }}}
{{{ x = 1000 }}}
1,000 ml of pure acid must be added
check answer:
{{{ ( 1000 + 125 ) / ( 1000 + 500 ) = .75 }}}
{{{ 1125 / 1500 = .75 }}}
{{{ 1125 = .75*1500 }}}
{{{ 1125 = 1125 }}}
OK