Mia can purchase a 40oz jar of peanut butter for $5.20 or a 15oz jar for $2.70. how much does mia save per ounce by buying the 40oz jar?

So you do price divided by ounces to figure out how much it cost per ounce

the 40oz would cost 13 cents an ounce

and the 15oz would cost 18 cents an ounce. 

just subtract 18 from 13= 5 

So you will save 5 cents per ounce by getting the 40 oz jar

Hope this helped :)