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My teacher is handing points to anyone who could guess how many pieces are in the construction shown below. I’d say there are about 350 but most people are saying thousand or more, which is insane to me. The only clues are that it is 43 cm long and 24 cm wide.

cactus christmas tree

How can I best go about such a task, i.e., how can I best estimate the number of pieces from a single photo?

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    It's not a set. Only the person who designed it knows how many pieces are in it. – Alexander O'Mara Dec 17 '17 at 2:22
  • I get it, but I just want someone with an actual knowledge on legos to make a good guess – Alain Llamas Dec 17 '17 at 3:25
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    Welcome to Bricks SE. I took the liberty to make the question more general. On Stack Exchange we hate to do your homework for you, but we may tell you how to do it yourself. – Wrzlprmft Dec 17 '17 at 11:05
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    She sent us a video as well, showing all sides of it. She just wants us to guess; the one who gets closer to the answer will have the extra points. So far I've meticulously tried to count (approximately) the pieces and I'd say there are about 619. Tomorrow we'll know who's won. – Alain Llamas Dec 17 '17 at 21:06
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    So...who won? Did the teacher give an actual full total, or her own guesstimate? Was it more about methods of estimation, or something else? The suspense is killing me! – Purplemur Dec 21 '17 at 19:32
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In this case, knowing that the model is 43 cm long and 24 cm wide isn't particularly information. It's very difficult to give a rough average of parts when all the parts vary in size and the model isn't in a single primitive form (cube, sphere, pyramid).

With the exception of the eyes and mouth, this particular model appears to be built almost perfectly symmetrically. If you can imagine a flat plane bisecting the model in two vertically you can count the bricks on the visible side (minus the details) and duplicate that number to get a rough guess.

The model could be mostly hollow, but there are bound to be certain pieces that you don't see on either side of the model that add to the physical structure. In particular the bricks that attach the eyes and mouth and the SNOT details on the arms.

In some places it can be a bit hard to visually count the bricks (particularly around the mouth). You can use basic image editing software to sharpen the image and get a clearer idea of how many parts are used.

There are also some unusual aspects in this model where three pieces have been used where a single 2x4 brick would do as shown at the top of the front side of plant pot.

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Couple of observations:

  1. I do not understand your teacher's motivations in giving out this exercise. There is too much guesswork involved to make the exercise of any educational value. Example: there is no visibility into the internal frame of the main "stem" of the cactus, which is clearly a SNOT build made of several layers of plates mounted on an (invisible) core supporting structure.
  2. Luckily, just putting in a guess is going to give you points, as the exercise is "My teacher is handing points to anyone who could guess how many pieces are in the construction shown below". Nowhere does it state that points are only handed out for correct guesses, so just guess any number and you should be fine.
  3. You have no insights into the back of the structure. This could be a mirror of the front (as suggested by @Ambo100) but it could also be constructed differently, without any way of telling. Similarly, you don't know if the pot structure is hollow or solid, or if the reddish brown earth is one plate or several layers thick.

In conclusion, either the teacher is trolling you, or you are trolling us with this question.

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    Probably just a fun extra credit exercise – JW8 Dec 17 '17 at 20:16
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    My son had a similar exercise this term to "Estimate the number of people in a crowd" with a fairly poor quality, black and white photo of a football stand. The goal was more about showing reasoning, and realising what was a reasonable estimate. There is educational value in this sort of task :) – Zhaph - Ben Duguid Dec 18 '17 at 10:34
  • @Zhaph-BenDuguid At the same time, people are all roughly the same size, and generally distributed rather uniformly in a crowd, so there are approaches which can leverage that. Neither applies to a Lego construction, so I see much less value in this guessing. – Angew Dec 30 '17 at 16:58

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