Well, let's set up an equation. You know you have 1/2 pound of trail mix total. You put 1/4 pound of trail mix into each bag-so how many bags do you have?
(1/4)x = 1/2
x refers to the number of bags you're trying to find. You're trying to get x by itself, so multiply both sides by 4.
You should get x=2, which means you filled 2 bags.