Each £5 note brings ten £10 notes with it, £105 a bundle. The rest has to be a whole number of £20 notes, and the only bundle count that leaves that is four: £420, with £380 left over, which is 19 twenties.
A customer asks the bank for £800 in notes: some £5 notes, ten times as many £10 notes, and the rest in £20 notes. How many of each does the cashier hand over?
Give me a hintThe hint
Count the £5 and £10 notes together, in bundles.