The better buy is the one that costs the least per pack of juice. If there are twelve packs of juice in the $3.90 package, then you would divide 3.90 by 12 to see how much each pack costs. If there are eighteen packs of juice in the $5.49 package, then you would divide 5.49 by eighteen.
After I did the math, I found out each pack in the 12-pack costs 33 cents, and each pack in the 18-pack costs 31 cents. So the 18-pack would be the better buy.
