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## Missing number

Posted by nordtorp on December 8, 2010 – 11:35 am

Find the missing number in this arragement

8 5 3
5 7 12
7 8 ?

This post is under “Tom” and has 27 respond so far.

### 27 Responds so far- Add one»

1. 1. cody Said：

15

2. 2. Rohan Said：

15

3. 3. Kenny Said：

I Say 1 or 15

4. 4. Wizard of Oz Said：

-1 by alternating – and + between the first two numbers
OR
5 by alternating mod 10 and mod 100 in the third number
OR
17 by incrementing the sums of the numbers by 16 each time
OR
21 by multiplying the sums of the numbers by 1.5 each time
OR . . .
Lots of numbers can be made to fit by any number of arbitrary operations.
I suggest more examples before the ? line.

5. 5. Chris Said：

Hey Wiz, you left out the families of polynomials that could fitted (LOL).

6. 6. nordtorp Said：

Another example is
8 5 3
3 10 7
5 7 12
7 8 ?

EDIT: Added an example to the problem

7. 7. Rajaneesh Said：

8. 8. Josh Said：

9

9. 9. Wizard of Oz Said：

Are we to assume that by calling post # 4 “another example” that the order of the examples doesn’t matter? In other words, is each example independent of the others so that there is no implied continuity between them?

10. 10. nordtorp Said：

Se post #4 again. I have changed it.

11. 11. KARL BUSH Said：

SHOULD BE -5

12. 12. Wizard of Oz Said：

OK, so it’s 13, based on the sums of each line incrementing by four: 16, 20, 24, then 28 (= 7 + 8 + 13).
This could not be deduced without the extra example.
Chris could doubtless find other answers from his polynomials.

13. 13. nordtorp Said：

Wizard of Oz and all you other. No one has the correct answer yet.

8 5 3
3 10 7
5 7 12
4 1 3
7 8 ?

14. 14. Kenny Said：

Its 10!!!

15. 15. rod Said：

5

16. 16. Jonte Said：

isn’t the answer to the original problem 5?

17. 17. nordtorp Said：

Nice try Kenny,

How did you find that number?

18. 18. Interesting Said：

I think the answer is either 1 or 15. i noticed that the 2 lowest numbers added up to the highest, but not in any specific order that i noticed.

19. 19. Ovva Said：

it’s 5

20. 20. B Said：

is it 5 ?

21. 21. B Said：

is it 5 for post #8?

22. 22. JBear Said：

I believe it is 15. It seems the most logical choice. I do agree a 1 could go in there, but I am sticking with 15. I am not sure why. As I said, it just seems the logical choice.

24. 24. mishu Said：

8 = 5 + 3
5 + 7 = 12
7 8 X

7 + X = 8 => X = 1

25. 25. nordtorp Said：

Some of you have mentioned the correct answer, but not with any good reason.

The answer is 1, just add up the odd numbers and you get the number.

5 + 3 = 8
3 + 7 = 10
5 + 7 = 12
1 + 3 = 4
7 + ? = 8

Missing number have to be 1.

26. 26. taquaya Said：

12. all have a match but 12.

27. 27. bunny Said：

its 15 because there fact families. 3+5=8 and so on.
therefor, 7+8=15 and so on.
it was pretty easy.

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