<PRE><B>Question 653610</B>
Let {{{ x }}} = fl oz of 80% solution needed
{{{ .2*6 = 1.2 }}} fl oz of acid in 20% solution
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{{{ ( .8x + 1.2 ) / ( x + 6 ) = .4 }}}
{{{ .8x + 1.2 = .4*( x + 6 ) }}}
{{{ .8x + 1.2 = .4x + 2.4 }}}
{{{ .4x = 1.2 }}}
{{{ x = 3 }}}
3  fl oz of 80% solution are needed
check:
{{{ ( .8*3 + 1.2 ) / ( 3 + 6 ) = .4 }}}
{{{ ( 2.4 + 1.2 ) / 9 = .4 }}}
{{{ 3.6 / 9 = .4 }}}
{{{ 3.6 = .4*9 }}}
{{{ 3.6 = 3.6 }}}
OK</PRE>