You don't say --- really

[ohioboy]

I bought a 15 can pack of diet coke (love it) and on the side it said "Three more cans than a twelve pack".

 

[Irwin]

... just in case you forgot your calculator.

 

[Judycat]

You'd be surprised how many people don't know that. They just grab the brick of soda and complain about the cost.

 

[Devi]

Or maybe it's a "wowie" sales pitch to get you to buy a bigger package.