Claire made 1⁄2 pound of trail mix. if she puts 1⁄4 pound of trail mix into each bag, how many bags are filled?

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.