Brain Teaser

[TransAmDan]

Brain Teaser
Three friends share a meal at a restaurant.
The bill comes to ?30
They divide it equally, paying ten pounds each.
But the waiter realises he's made a mistake and should have charged ?25.
He gives the friends five pounds back .
They decide to take one pound each and give the waiter a ?2 tip
So, each person ends up paying ?9 and the waiter keeps ?2, making ?29 in total.
What happened to the missing ?1?

 

[TransAmDan]

The Answer
There is no missing pound.
You don't add the ?2 to the ?27 they've paid because the ?2 is already included in that ?27 - The ?2 features twice
The actual sum is the ?27 plus the ?3 they got back, which brings you to the original ?30.
The premise of the question is false!