Keep The Change
Riddle: A man pays for his lunch with a £10 note. The lunch costs £7 and the waiter who is bringing him £3 change decides to pocket £2 and hand him only £1. Now the diner has received £1 back from £10 and has so paid £9. The waiter has kept £2, making £11 in all. So, where did the extra £1 come from?
Answer: There is, in fact, no extra pound. The way to think of it is this: the man paid £7 for his meal, the waiter took £2, and the man kept £1 in change: £7+£2+£1=£10. The riddle is phrased so that the £2 tip appears to have been added to the £9 which the diner is out of pocket, when, in fact, it should be subtracted from it.
Source: https://www.riddles.com/11688
