# Online IQ test question - which number doesn't belong?

I took an online IQ test(www.free-iqtest.net) and encountered this problem which I wasn't able to do: I know that the answer is EIGHT but I do not know why the number 8 doesn't belong in the series. I was just lucky and guessed it correctly. I want to know why the answer is EIGHT. Thank you.

## 3 Answers

The logic of this series is number +1(for the number after it) and ×2(for the number after that number). Using this, the second number is 2+1=3, the third number is 3×2=6, the fourth number is 6+1=7, the fifth number is 7×2=14, the sixth number is 14+1=15, and the seventh number is 15×2=30. 8 cannot be after 7 since 7×2≠8. Therefore, 8(EIGHT) does not belong in the series.

• Can you please explain this further? With words? Also, we have a policy that the important parts of answers should be in spoiler (>!) blocks, please add that. – bobble Oct 31 '20 at 4:38
• This answer is extremely logical and you did an extremely good job in explaining the logic behind the series. However, your answer isn't very clear and you should explain this further and use words, like what bobble said. You should also hide your explanation with spoiler blocks(>!), like what bobble said. – user72139 Oct 31 '20 at 4:50
• @pilotjoker999 thank you for the edit – Aakash Mathur Oct 31 '20 at 5:06
• @AakashMathur no problem – Pilot Oct 31 '20 at 5:09

One possible answer is that

all of the other numbers in the sequence are either 2 or 3 modulo 4. (That is, if you divide by 2 and round down, the result is odd.)

But there are likely multiple other answers.

Highlighted in yellow are the numbers that appear consecutive. We can see that the numbers 6, 7 and 8 are the only consecutive numbers that have 3 numbers in it. The other consecutive numbers only have 2 numbers in them. By removing 6 or 8, we answer the question. Therefore, the answer is 8(EIGHT) since 6(SIX) is not an option in the options.

• I thought about that... but what about 30? I wasn't sure how to deal with 30 either -- with my idea, there's an even nicer pattern if you ignore it too. But if it's just consecutive sequences, wouldn't it be more natural to remove 30? – Deusovi Oct 31 '20 at 3:00