# Which duplo digit is 6 or 9?

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?

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

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

Ergo

The green is 6 and the purple is 9.

• Very helpful to draw the studs :) Commented May 19 at 14:42
• Alternative reasoning: rot13(oybpxf ner pbyberq va ebltovi beqre) Commented May 20 at 13:26
• This matches what is currently being sold by LEGO. Commented May 21 at 15:08
• @EngineerToast, that is exactly the set we have :) Commented May 21 at 16:11
• 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.
– 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.

Because:

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.

• 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 :) Commented May 22 at 19:35
• This wasn't from looking it up, but I did validate my answer before posting :) Commented Jun 3 at 13:27