Question 936976
Let {{{ x }}} = ounces of pure acid to be added
{{{ .4*35 = 14 }}}  ounces of pure acid in 40%
solution
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{{{ ( x + 14 ) / ( x + 35 ) = .7 }}}
{{{ x + 14 = .7*( x + 35 ) }}}
{{{ x + 14 = .7x + 24.5 }}}
{{{ .3x = 10.5 }}}
{{{ x = 35 }}}
35 ounces of pure acid needs to be added
check:
{{{ ( x + 14 ) / ( x + 35 ) = .7 }}}
{{{ ( 35 + 14 ) / ( 35 + 35 ) = .7 }}}
{{{ 49 / 70 = .7 }}}
{{{ 49 = .7*70 }}}
{{{ 49 = 49 }}}
OK