How can the make money?

I just got back from a drive and on the way I picked up a snack for my daughter and I.
She got a mighty kids and I got a Big Mac. Yes I still eat those nasty things.
I went through the drive thru, ordered and was asked if I wanted 2 Big Macs for $2.40?
"How much is one?"
"$2.37"
Huh! 3 cents for the second Big Mac. Aside from the fact that it will likely kill me this is a no brainer deal.
Luckily the kid has a bottomless pit for a stomach so she got the second one.