They each order the same - a full english breakfast and a pot of coffee.
This comes to exactly £5.00 each, totalling £15.
At the end of the meal, they each throw in a £5 note and give it to the waitress. She takes the £15 to the till, where the manager informs the dozy mare that there is a special offer on today only - full english and a pot of coffee for £4.
The waitress puts the money into the cash drawer and takes out 5 pound coins. She walks back to the table and gives each of the 3 students a pound back. Being a thieving gypsy, she then pockets the remaining 2 pound coins.
To summarise - the students, having received a quid back each, have paid £4 each for their meals.
3 x £4 = £12
The tea leaf waitress pocketed £2
£12 + £2 = £14
Where has the other pound gone?
Beacuse essentially, as Dringo says, the puzzle is about keeping track of where you should be adding and subtracting the money.
Ammount paid by group = Ammount in til + Ammount half-inched by tea leaf
(just to confuse matters more ;^) )
£15 Paid originally = £10 in til + £5 taken out by waitress
£12 paid = £10 in til + £2 in pocket
I like the puzzle as it teaches you the imporance of actually thoroughly understanding what's happening in a mathematical problem, instead of just moving the numbers in a way that seems right. Sometimes easier said than done.
This kind of 'slight of reasoning' is also used in a scam where you go into a shop and buy something of small value with a note, then try to make up the money with change, and in the confusion', you come out ahead.
Someone tried it on me once when I was working in a petrol station a few years ago. It was only because I knew of the move already that it didn't work on me.
Even then I wasn't convinced the guy had actually done it intentionally (he pulled it off very smoothly, obviously well practiced!). Although when I told him 'that doesn't work', the way he tripped over himself apologising and getting out of the shop suggested he might have known what he was doing.
As it happened everyone else got it and I didn't.
The kids paid £12... we've counted that... the "£2" has nothing to do with it. She just nicked it from the till.
Already seen that thanks. Read 'The Three Stigmata of Palmer Eldritch', that'll keep you thinking.
And it is about counting money twice.
In your story you say that the students paid £12. The £2 is part of that, it is arbitury (Sp).
The two pounds that the waitress has kept is part of the 15 pounds that was in the till - it is not different money, so it can't be added to the £12 the customers have paid.
See? Counting money twice.