Question 935672
{{{ 1/100 }}} = ( liters disinfectant ) / ( water )
{{{ 5 }}} liters = disinfectant + water
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Liters of water = 5 - liters of disinfectant
Let {{{ x }}} = liters of disinfectant
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{{{ 1/100 = x / ( 5 - x ) }}}
Multiply both sides by {{{ 100*( 5 - x ) }}}
{{{ 5 - x = 100x }}}
{{{ 101x = 5 }}}
{{{ x = .0495 }}} liters 
Ana needs 49.5 ml of concentrate
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check:
{{{ 1/100 = x / ( 5 - x ) }}}
{{{ 1/100 = .0495 / ( 5 - .0495 ) }}}
{{{ .01 = .0495 / 4.951 }}}
{{{ .01 = .009998 }}}
close enough