Buy One, Get One Free a From Thought

(A customer presents me with a buy one get one free for a burger.)

Customer: “How much would this come to?”

Me: “That’s [price].”

Customer: “Okay, and how much would it be if I didn’t use the coupon and only got one burger?”

Me: *That’s [same price].”

Customer: “But how come it’s the same price?”