Mysteries of ATMs

I withdrew cash from an ATM today. Nothing unusual about that, and indeed there wasn’t anything unusual. However, there is something that has always interested me vaguely. More intrigued than interested, perhaps.

Unless I need more, I withdraw £30. The main reason is that cash machines almost always give out three £10 banknotes, and not one £20 note and a tenner. Don’t ask me why, but I prefer to carry £10 notes than £20 notes. Given the experience so far, I assume the machines are programmed to dispense three £10 notes when a customer requests £30.

The odd thing is that when I withdraw £20, sometimes the machine gives me one £20 note and sometimes two £10 notes. Even the same cash machine. I was theorizing that the ATM decides which note(s) to dispense depending on how many notes of each denomination it has still inside, but if that were the case, then that should apply to the withdrawals of £30 as well.

May be, and just may be, the next time I withdraw £30, the machine will give me a £20 note and a £10 note.