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Multiple Magic
Age 11 to 14
ShortChallenge Level 
Think of any whole number.
Double it and add five.
Double this answer and add two.
Now take away the number you first thought of.
Your answer will always be a multiple of which number?
If you liked this problem, here is an NRICH task which 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.
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