Question 1047032
Let {{{ x }}} = % of the 1st solution needed
{{{ ( x*10 + .4*9 ) / ( 10 + 9 ) = .41 }}}
{{{ 10x + 3.6 = .41*19 }}}
{{{ 10x = 7.79 - 3.6 }}}
{{{ 10x = 4.19 }}}
{{{ x = .419 }}}
41.9%  is the acid concentration of the 1st solution
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check:
{{{ ( x*10 + .4*9 ) / ( 10 + 9 ) = .41 }}}
{{{ ( .419*10 + .4*9 ) / ( 10 + 9 ) = .41 }}}
{{{ ( 4.19 + 3.6 ) / 19 = .41 }}}
{{{ 7.79 = .41*19 }}}
{{{ 7.79 = 7.79 }}}
OK