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There are lots of ways of choosing three dots from this $4$ by $4$ array.
How many triples of points are there where all three lie on a straight line (not necessarily equally spaced)?
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.