1, 1, 2, 3, 4, 5, 8, 13, 21 – Which one doesn’t belong to this series?
The sequence presented is as follows: 1, 1, 2, 3, 4, 5, 8, 13, 21. Can you identify which number does not belong to this series, and explain the reasoning behind your choice?
10 Answers
This is a Fibonacci number
we know that
1
1 + 1 =2
1 + 2 = 3
2 + 3 = 5
3 + 5 = 8
5 + 8 = 13
13 + 8 = 21
Therefore the number doesn't belong to this series is 4....
21-13=8
13-8=5
8-5=3
5-3=2
3-2=1
2-1=1
now you decide which number
does not belong to this set of numbers.
This is a fibonacci series every number is the sum of the previous two numbers. the 5 does not belong.
Everyone thinks it is funny to give you the wrong answer 4. Don't let them make fun of you. The correct answer is 5. The people who answered think it is far more important that they look smart than it is that you try to figure it out and actually learn.
Dec 05, 2024
If you take out the 4, you have the start of the Fibonacci Sequence, which is defined as each term is defined as the sum of the previous two terms (Except the first 2 terms which are each 1)
So the 4 doesn't belong.
Dec 06, 2024
First, that's a sequence, not a series, since there are no addition signs.
Second, any answer can be justified, for example 1 doesn't belong because it's the only number that's repeated, or 21 doesn't belong because the rest of the numbers aren't divisible by 7, etc.
However, I do notice that this sequence looks exactly like the Fibonacci sequence, except that 4 is not part of the Fibonacci sequence. In the Fibonacci sequence, the first two numbers are 1, and every other number is the sum of the two previous numbers. So in that case, the answer is 4.
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