When taking an IQ test, the set of numbers given is:

17, 12, 108, 9.

You are supposed to work out which number does not fit. I have earmarked 17 as the incorrect number for two different reasons: it's the only number not divisible by 3, and it's the only number not divisible by another number in the sequence (i.e. 108÷12=9) - but the test keeps saying that's not the correct answer.

Please help me determine which number does not fit, and why.

  • 5
    $\begingroup$ What is the question exactly? To choose the odd one out among these numbers? Is it just an unordered set of numbers, or a sequence where the order is important? $\endgroup$ Commented Jun 11, 2023 at 14:39

2 Answers 2


As @Randal'Thor mentioned in the comments, it's not fully clear whether this is simply a set of numbers or really a sequence where order matters. Since it is not asked for the next number, this looks to me more like a simple "odd one out". For me there is no "obvious" solution and I am sure you could think of many more reasons why one number is the "odd one out".


- it is the only prime number

- it's the only number with an even cross sum


- the last digits are increasing 7,8,9 but the 2 of 12 doesn't fit


- as @IlCorsaroNero mentioned it's the only number increasing the otherwise falling sequence


- because it is the only number which doesn't start with 1

  • 6
    $\begingroup$ In other words, odd-one-out puzzles with just a bunch of numbers are a bad puzzle/ question format in general. Any answer is correct and this just becomes a 'guess what I am thinking' puzzle. $\endgroup$
    – quarague
    Commented Jun 13, 2023 at 13:12

For me the incorrect number is :

108 because the number are decrease but 108 is the only number the increase the sequence.


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