Why is buying something with lower cost per ounce somehow cheaper or a better deal than buying something with a higher cost per ounce, even if the total price is higher for the lower cost per ounce product?

Question

Why is buying something with lower cost per ounce somehow cheaper or a better deal than buying something with a higher cost per ounce, even if the total price is higher for the lower cost per ounce product?

In:

Answer 1

Let’s say I’m buying bottled water. One bottle costs two dollars, while 20 bottles fifteen dollars. Since I know I’m going to need more than 20 bottles over the course of my life, as water is rather necessary, I know that I will end up buying at least 20 bottles no matter what. I can either buy a single bottle 20 times which costs forty dollars, or I can buy the 20 pack once for fifteen bucks.