In order to find which one is a better deal, we need to find the cost per unit. The way to find this is take the cost and divide it by the number of units. Our single unit in this case is an ounce, so we will find cost per ounce.
The 8 oz bag:
[tex].64\div8oz =.08/oz[/tex]
8 Cents Per Ounce
The 20 oz bag:
[tex]1.28\div20=.064[/tex]
6.4cents per ounce
So, the 20 ounce bag is a better deal since its cost per ounce is less.