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Re: 1, 1, 2, 3, 5, 8, 13, 21, 34, . . . [#permalink]
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Yes it is B

Correct both the answer and the approach
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Re: 1, 1, 2, 3, 5, 8, 13, 21, 34, . . . [#permalink]
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AkmKawser wrote:
F11=F9+F10 = 34+55 = 89
Thus Quantity B is Greater. Answer: B


The answer is B and it's simple. But I want to give a detailed explanation of this so that other similar problems can be tackled. So here we go.

1st of all this is neither a Geometric nor Arithmetic Sequence so we can't use any of those tricks here. We have to build it using the basic concept of defining Sequences.
If we think of it in an inductive way :
We have to think about it in a bottom-up manner. We have to think about it in terms of the 1st term and start building up to the bottom until we reach F11.

F3=F1+F2
F4=F2+F3
F5=F3+F4
....
F11 = F9+F10

If we think of it in a deductive way:
We have to think in a top-down manner. Breaking the actual problem into previous terms. So we start with F11 right away.
F11 =F9+F10
= {(F7+F8)+(F8+F9)}
= .........until we reach the base case.

In either case, the formula is simple as I have shown.



I don't agree since the pattern does not suggest the sequence is as we see it. I just had a similar problem.


"I did the same mistake assuming I've gotten the pattern but the answer was very revealing:

The reason is that there's no way that we can definitively determine ONE (and ONLY ONE) pattern in a given sequence.

Consider this example: 1, 2, 4, __
What's the missing term here?
Well, if we read the sequence as doubling from one term to the next, the next term is 8
HOWEVER, if we notice that we keep adding successively larger integers to each term (i.e., add 1, then add 2, then add 3, etc.) the next term is 7

Likewise, (if we want to get a bit silly), we might look at the given sequence (5, 10, 15, 20, 25, __) and say that the next term is 88. Why?
Because 5 is my favorite number, 10 is my 2nd favorite number, 15 is my 3rd favorite number, ... and 88 is 6th favorite number.

So, although you might have found a certain pattern in the sequence (double and add 1), we can't be certain that this is THE pattern.
This means t_5 can have ANY numeric value.
"
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Re: 1, 1, 2, 3, 5, 8, 13, 21, 34, . . . [#permalink]
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