Question 757087
Let {{{ x }}} = ml of acid to be added
{{{ .15*50 = 7.5 }}} ml of acid in 15% solution
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{{{ ( 7.5 + x ) / ( 50 + x ) = .25 }}}
{{{ 7.5 + x = .25*( 50 + x ) }}}
{{{ 7.5 + x = 12.5 + .25x }}}
{{{ .75x = 12.5 - 7.5 }}}
{{{ .75x = 5 }}}
{{{ x = 6.667 }}}
6.667 ml of pure acid must be added
check:
{{{ ( 7.5 + x ) / ( 50 + x ) = .25 }}}
{{{ ( 7.5 + 6.667 ) / ( 50 + 6.667 ) = .25 }}}
{{{ 14.1667 / 56.667 = .25 }}}
{{{ 14.1667 = 14.1667 }}}
OK