## Question 4 - Bonus

This trick is based on the number of matches in a matchbook.

- Take an unused matchbook that contains 20 matches and tear out any number of matches, up to 9.

- Throw them away and count the matches that remain.

- Add the 2 digits of this number and tear out the same number of matches from the book.

- Tear out 2 more matches
Try this a couple of times. What is the result?

Think of a way to prove the answer will always be the same. You do not need to use algebra if you can find another method.

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28 January 1996