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Fri 4 Apr, 2003 03:01 pm
What's next in the following sequence?
3, 5, 7, 9, ___
Scroll down for the answer
Yes, you already figured there is something tricky about it.
Actually, the sequence can be practically anything! Just as an example,
I will take the number 66 as being next in the ___. Yes, I know
you're going "Huh? I thought it is 11!" Well, it is, but it's also 66
and any other number you can think of! Here's why:
Let's say we have a function a(x), b(x), c(x), d(x), and e(x).
a(x) = (x-2)(x-3)(x-4)(x-5)/((1-2)(1-3)(1-4)(1-5))
As you can see, a(1) = 1, a(2) = 0, a(3) = 0, a(4) = 0, a(5) = 0
We proceed like this with b(x)-e(x), but replace 1 with 2-5:
b(x) = (x-1)(x-3)(x-4)(x-5)/((2-1)(2-3)(2-4)(2-5))
c(x) = (x-1)(x-2)(x-4)(x-5)/((3-1)(3-2)(3-4)(3-5))
d(x) = (x-1)(x-2)(x-3)(x-5)/((4-1)(4-2)(4-3)(4-5))
e(x) = (x-1)(x-2)(x-3)(x-4)/((5-1)(5-2)(5-3)(5-4))
Now the polynomial y(x) is going to go like this:
y(1) = 3, y(2) = 5, y(3) = 7, y(4) = 9, y(5) = 66
And here is how we do it:
y(x) = 3(a(x))+5(b(x))+7(c(x))+9(d(x))+66(e(x))
When this polynomial is simplified, we simply get:
y(x) = 55/24*x^4 - 275/12*x^3 + 1925/24*x^2 - 1351/12*x + 56
Try entering 1, 2, 3, 4, and 5 as x into this polynomial and
gape at the unexpected results!
This is why I'm concerned that sozobe's riddle does not present the unerlying logic correctly.
Does it also exclude all other answers?
Yep, there is one specific answer.
sozobe, one answer is better than the other. There are infinitely many answers to your riddle, but I bet you have one that is better than the others, and that's what counts. We have thought of millions of ways to cure cancer, and all we possibilities, but some worked better than others. So far, we're still searching for better ones, because cancer is still a problem.
Oh, just saw this.
No, there's one specific answer. I mean, by the logic shown here, it -could- be any number, I guess, but that's not what I have in mind with the riddle. One specific answer.
Hi,
What is the puzzle you are talking about?
Could you quote it for me?
Laura
sozobe's number riddle (it's called "Number riddle I made up")