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A square is divided into eight congruent triangles, as shown.


Two of these triangles are selected at random and shaded black.

What is the probability that the resulting figure has at least one line of symmetry?

 
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.