<PRE><B>Question 1136343</B>
Let {{{ x }}} = ml of 9% solution to be added
{{{ ( .02*70 + .09*x ) / ( 70 + x ) = .07 }}}
{{{ 1.4 + .09x = .07*( 70 + x ) }}}
{{{ 1.4 + .09x = 4.9 + .07x }}}
{{{ .02x = 3.5 }}}
{{{ x = 175 }}}
175 ml of 9% solution should be added
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check:
{{{ .02*70 = 1.4 }}}
{{{ .09*175 = 15.75 }}}
{{{ ( 1.4 + 15.75 )/( 70 + 175 ) = 17.15 / 245 }}}
{{{ 17.15 / 245 = .07 }}} ( 7% )
OK
</PRE>