Question 567250
Let {{{ x }}} = liters of pure acid to be added
{{{ .1*4 = .4 }}} liters of acid in 10% solution
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{{{ ( x + .4 ) / ( x + 4 ) = .8 }}}
{{{ x + .4 = .8*( x + 4 ) }}}
{{{ x + .4 = .8x + 3.2 }}}
{{{ .2x = 3.2 - .4 }}}
{{{ .2x = 2.8 }}}
{{{ x = 14 }}}
14 liters of pure acid is needed
check:
{{{ ( x + .4 ) / ( x + 4 ) = .8 }}}
{{{ ( 14 + .4 ) / ( 14 + 4 ) = .8 }}}
{{{ 14.4 / 18 = .8 }}}
{{{ 14.4 = .8*18 }}}
{{{ 14.4 = 14.4 }}}
OK