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Age 14 to 16 Short Challenge Level:

Which of the five diagrams below could be drawn without taking the pen off the page and without drawing along a line already drawn? Can you explain your reasoning?

If you liked this problem, here is an NRICH task that challenges you to use similar mathematical ideas.

This problem is taken from the UKMT Mathematical Challenges.
You can find more short problems, arranged by curriculum topic, in our short problems collection.