Question 1015055
Let x = # cc of the 40% concentrate.
Then 1000 - x = #cc of the 60 concentrate.

==> 0.40x + 0.60(1000- x) = 0.55(1000)

0.40x + 600 - 0.60x = 550
-x/5 = -50

x = 250 cc of the 40% concentrate, and
750 cc of the 60% concentrate.