### Brain Teasers

# Which number doesn't belong?

Group
These brain teasers rely on your ability to recognize groups of common attributes. For each of these puzzles you'll need to figure out why the words or letters are grouped as they are. Sometimes you will be asked to pick the odd-one-out or to place a new word into the correct group.Group

Which number doesn't belong?

3

19

17

23

29

51

11

7

13

5

97

3

19

17

23

29

51

11

7

13

5

97

### Hint

Remember your math.### Answer

51 does not belong because it is the only number that is not prime.A prime number has only itself and 1 as factors. 51 has 4 factors: 1, 3, 17, and 51.

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## Comments

The key to this one is to study a Math Primer...then one is sure to get it right.

i knew it was the prime rule, i just didn't know that 51 is plrime thats all

51 isn't prime that's why it is the odd one out.

excellent teaser... the prime number factor is the first thing i checked for and it was rite... might not be so easy for others

YAY i actually got one wooo

I found this one quite easy, but I'm a math guy so the pattern jumped at me. I did have to ponder 97 for a bit to confirm it is prime. Good simple teaser.

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