Note that the puzzle didn't ask for three digits to be circled!
Three people check into a hotel. They pay £30 to the manager and go to their room. The manager suddenly remembers that the room rate is £25 and gives £5 to the bellboy to return to the people. On the way to the room the bellboy reasons that £5 would be difficult to share among three people so he pockets £2 and gives £1 to each person. Now each person paid £10 and got back £1. So they paid £9 each, totalling £27. The bellboy has £2, totalling £29. Where is the missing £1?
Hint: Be careful of what you're adding.
We have to be careful what we are adding together.
Originally, they paid £30, they each received back £1, they now have only paid £27. Of this £27, £25 went to the manager for the room and £2 went to the bellboy.
Can you draw a line through all of the edges in this picture?
Each side is broken into 2 or 3 edges, and there are also 7 edges inside that you have to cross. The line must be continuous, and cross each edge exactly once.
Hint: Try this with a piece of paper.
There is no possible way to complete the line, there will always be one edge left - or you have to cross an edge twice. This puzzle is the same as the famous 'Seven Bridges of Konigsberg' problem first solved by Euler. In that problem, the task was to find a closed path that crossed each of the seven bridges of Konigsberg (now Kaliningrad, Russia) exactly once.
How can you get ten horses into nine stables, one per stable?
[Ref: ZNSN] Submitted by Justin Thomas.
Hint: You may have to think a little laterally.
Answer: Place one letter from TEN HORSES into each of the nine stables.