Originally published at: https://boingboing.net/2020/01/30/how-many-triangles-do-you-see.html

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I see nine.

18?

I keep thinking I am missing some though.

ETA and now done with the Popular Mechanics article and indeed 18.

Well I thought it was pretty straight forward but when posed as a brain teaser I want to over think it.

ETA More now that I can get to the meme site.

Same here. Almost sure it’s 18.

Does it still count as a ‘triangle’ if there is a line segment connecting the midpoints of two sides?

Or is that just a trapezoid that shares a side with a triangle?

But, yeah, I get 18.

18

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18, unless the lines on the paper also count, then … lots.

I SEE all of them…

A triangle is a figure with 3 straight edges. All the straight lines in this picture are parallel. No triangles here. QED.

I got 16 initially, read the comments here, had to go back and figure out which two I had missed, yep 18.

One large triangle containing lines, and 3 interior triangles within those lines. To find more you have to imagine some lines don’t count as lines.

That’s my contrarian opinion and I’m sticking to it.

But nobody will agree.

Yep. The enclosed form’s lines aren’t straight. So, I also see no triangles.

How many circles do you see here?

I would say “three” but if I’m reading your opinion right, the orange circle is no longer a circle because there’s something inside it. Are you sticking to it?

36

(and some filler for the comment)

I get 20 in a somewhat sneaky way:

18 as illustrated in the pop mech solution, Plus two small triangles found in the capital letters A in the question.i

Did you include the horizontal lines which turn each of the other triangles into 3 triangles

Laurel. No, white and gold!

Looking at the drawn on lines there are 18. I’m getting an additional 30 give or take when you incorporate the ruled lines. So 48 ish

The answer is actually 20.

Don’t forget to count the capital As.