Not every question has to be as hard as possible, here is an easy one.

I joined my kids playing with duplo, and found out that the duplo 9 and 6 look exactly the same if you turn one of them 180 degrees. So I decided to build the structure below. Of course I didn't use any glue or tape. Could you reason which of the following digits is the 9 and which is the 6?



4 Answers 4


If the green is 9 it would lead to this scenario:

enter image description here

As you can see the yellow and green bricks on the bottom left are unsupported and would fall away down…


The green is 6 and the purple is 9.

  • 2
    $\begingroup$ Very helpful to draw the studs :) $\endgroup$
    – Lezzup
    Commented May 19 at 14:42
  • 2
    $\begingroup$ Alternative reasoning: rot13(oybpxf ner pbyberq va ebltovi beqre) $\endgroup$
    – qdread
    Commented May 20 at 13:26
  • 1
    $\begingroup$ This matches what is currently being sold by LEGO. $\endgroup$ Commented May 21 at 15:08
  • $\begingroup$ @EngineerToast, that is exactly the set we have :) $\endgroup$
    – Lezzup
    Commented May 21 at 16:11
  • $\begingroup$ One of the things that was not obvious to me was that the construction was being held up, and therefore, pieces could fall down. Instead, I imagined it lying flat on a table, which makes either configuration possible. @Lezzup 's picture forces the intended perception. $\endgroup$
    – JLee
    Commented May 22 at 14:52

Because the correct answer is already given, here is the other photo I took, that explains everything without words:



Green is 6, purple is 9.


if it was the other way round (green 9 and purple 6), then nothing would hold the left (white-yellow-green-yellow) and right (red-red-yellow-blue) sides of the structure together, and the left side would fall away since you're only holding the right side.


Insight: the numbers are colour-coded onto a rainbow.

Green is in the centre of the rainbow, violet is at the end.

6 is near the centre of the digits, 9 is at the end.

Therefore the 6 is green, the 9 is violet.

Duplo Train with spectrum of colours

  • $\begingroup$ This is more like cheeting in my opinion. I had thought about it to explicit put the instruction there, to not look it up... but yeah, this answer is technically correct, and we have actually this specific duplo set :) $\endgroup$
    – Lezzup
    Commented May 22 at 19:35
  • $\begingroup$ This wasn't from looking it up, but I did validate my answer before posting :) $\endgroup$ Commented Jun 3 at 13:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.