Ok 30 - 5 + 5 = 29
3 friends decide to buy a radion which is £30. So they all pay £10 each and leave the shop with the Radio
Manager comes down and asks the Sales girl "How much did you sell the Radio for"
Sales Girl replies "£30 like it said on the tag"
Manager "it should have been reduced to £25 take £5 from the till and quickly go and give them the refund"
Sales girl takes £5 but as she is running after them she realises that £5 won't go equally into 3 so she takes £2 for herself and gives them £1 each back.
So the sums are as follows
£30 for Radio / 3 = £10 each
Each man is given £1 back = £3
Sales Girl Keeps £2
Each man spent £9 meaning they spent £27 (£10 - £1 x 3)
Sales girl has the other £2 so the Total is now £29
Voila 30 - 5 + 5 = 29