It's like those trick questions we got at school. Not only were they testing your maths, they were seeing how smart you were to work it out.

If it was laid out like a bill, it would go something like this for each man:-

£8.33 bar tab

£0.67 for the bar back.

£1 overpayment =

£10 in total

OR if you prefer:-

£10 paid on account.

£8.33 bar tab

£0.67 for the bar back =

£9.00 to pay, £1 overpayment returned = £10.

OR if you prefer this way:-

£30 paid on account.

£25 bar tab

£2 for the bar back

£27 in total due. £3 overpayment returned = £30