# Which of these numbers does not belong to the group?

I thought this was easy, but cute, so I decided to share it:

1011, 2223, 3940, 5648, 8910

5648

The other numbers are

adjacent numbers concatenated to each other:
1011 = 10, 11
2223 = 22, 23
3940 = 39, 40
8910 = 8, 9, 10

Here's an alternate answer that is also valid

2223 is the odd one out.

This is because each of the other numbers contain 'holes' (closed loops in the digits), i.e at least one of the digits 4 6 8 9 0 is present in the numbers.

• Yeah, this works too:) It seems will have to tweak my numbers again... Jul 20 '15 at 6:16

At the risk of being downvoted for giving an answer different from the accepted one:

Can also be said 2223, because the numbers form a non-descending series.

5648

Explanation:

The members are base 10. And each digit in each member is within one of another digit in the member. Assuming this 0,1,2,3,4,5,6,7,8,9,0,... line of digits, one move in either direction. 5648 contains an '8' and would need either an additional '7' or '9' to fulfil the property.

• I don't understand what you mean by "each digit is within one of another digit". Can you please clarify? Jul 20 '15 at 19:52
• @mmking I edited it. Jul 20 '15 at 20:02
• I still don't understand. Jul 21 '15 at 8:01
• I edited for additional clarification. I hope the example will suffice. Jul 21 '15 at 12:22
• Every number that follows the accepted answer's criterion also satisfies this one, but not vice versa, e.g. 5647.
– f''
Jul 21 '15 at 12:34