So we have a star, a mountain and another shape today. Our job is to carefully count all the triangles in each of them.

I encourage you to give this problem a try, and when you are ready, keep reading for the solution.

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Solution

Of course there are 5 triangles. But there’s more!

This is a bit trickier because some might think there are only 3 more triangles, when there are in fact 5 more. So 10 triangles for our star.

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There are 4 triangles of the this size.

There are 3 triangles of this size.

There are 2 triangles of this size.

And only 1 triangle of this size. 4 + 3 + 2 + 1 = 10. So 10 in total.

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There are 5 triangles on their own.

There are 4 triangles made of two parts.

There are 2 triangles made of three parts.

There’s 1 triangle made of five parts. 5 + 4 + 2 + 1 = 12, so 12 triangles!

Did you count them all?