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'Weekly Problem 40 - 2010' printed from http://nrich.maths.org/

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The diagram shows nine points in a square array. What is the smallest number of points that need to be removed in order that no three of the remaining points are in a straight line?

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.

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