[CookWithMe]

I have never used a gift card at starbucks before, but that bill [0] doesn't make any sense to me.

He says he has two cards: One has $15, one has $5.

Card 3203 is billed $14.68 and card 6075 is billed $2.02.

The remaining balance on card 3203 is $0, card 6075 has $5.70 remaining.

If card 3203 had $15 and card 6075 had $5 before he used them, the remaining balance should have been $0.32 and $2.98, respectively...

That's really me guessing, but it could be the $5 was just an example to explain the concept and in fact he used smaller values (e.g. $0.05) to be able to trigger the bug more often without generating too much cash... but he should have explained the bill somehow.

[0] http://sakurity.com/img/sbcheck.jpg

[cokernel]

That's exactly right. In the comments Homakov mentions that the $15 and $5 figures have been "adjusted for simplicity".