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Missing Digit
Age 11 to 14
ShortChallenge Level 
The 8-digit number 1234_678 is a multiple of 11.
What is the missing digit?
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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