SOLUTION: 3, -6, 12, 4, 20, ? 7, 16, 8, 27, 9, ? 2, 7, 26, 101, 400, ? 7, 21, 8, 72, 9, ?

Question 1121010: 3, -6, 12, 4, 20, ?
7, 16, 8, 27, 9, ?
2, 7, 26, 101, 400, ?
7, 21, 8, 72, 9, ?

Found 2 solutions by greenestamps, Alex.33:
Answer by greenestamps(13200) (Show Source): You can put this solution on YOUR website!

There is no mathematics involved in these problems, or any problems like them.

Given ANY finite sequence of numbers, you can put ANY number next and it will be a valid sequence.

The ONLY way to know the "RIGHT" answer to ANY problem like this is to ask the author of the problem what the answer is.

I would recommend spending only a minute or so (at the most) on any problem like this to see if you can see a logical pattern that might predict the next number. However, while that might give you some good mental exercise, in the end you have no idea if your answer is right, because the author of the problem might have used a different logical pattern.
Answer by Alex.33(110) (Show Source): You can put this solution on YOUR website!
First line:
3-9=-6 -6+9*2=12 12-8=4 4+8*2=20
hence a possible solution(I'll give two from the end of the line): 20-7=13 13+7*2=27
Second line:
7+9=16 16-8=8 8+19=27 27-18=9
hence a possible solution: 9+29=36 36-28=8
Third line:
2*4-1=7 7*4-2=26 26*4-3=101 101*4-4=400
hence a possible solution: 400*4-5=1595 1595*4-6=6374
Final one:
7*3=21 7+1=8 8*3^2=72 8+1=9
hence a possible solution: 9*3^3=243.
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I totally agree with Greenestamps. I just did it according to the most common pattern of similar questions I have encountered, yet I have to say these sequence problems appearing in exams are no more than meaningless stuffs. There's nothing to be tested in them and they can only be an indicator of whether your thoughts coincided with the author.
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