Question 331347
Let x=number of liters of mixture to be drained.

We drain out x amount of the 40% and then add back the same amount of pure.

So, we have the equation {{{.40(6-x)+x=.50(6)}}}

{{{2.4-.40x+x=3}}}

{{{2.4+.60x=3}}}

{{{.60x=.60}}}

{{{x=1}}} liter.