(no subject)

[arethinn]

What three numbers follow in this pattern?

4 8 12 7 19 6 25 5 ...

correct answer was D. 30 4 34. I can see that there's adding going on here - 4+8=12, 12+7=19, 19+6=25, but I'm lost as to how they got from 12 to 7, 19 to 6, etc. Is it just that every second number is counting down from 8?

Comments

[nicanthiel]

Yes, they're adding up and then counting down. The next sets should be 38 3 41 2 43 1.

[arethinn]

I hate number pattern puzzles. I'm terrible at them :P

[foxgrrl]

I have a rant about these kinds of stupid sequence prediction questions they put on standardized tests. I'll just give you the summary here: The next number in the sequence could be anything! For example: 2,4,6,8,__ What's the next number in the sequence? Most people would say 10, but it's actually 16, because these are the numbers, N, such that 7*2^N - 5 is prime. Or actually, maybe the answer is 22, because all digits are even and non-zero. Or possibly 20, if the sequence is the totients of consecutive pure powers of primes.

Really, all these things do is test how closely you think like the test's author.

Anyway, no one seems to have heard of this sequence before...
http://oeis.org/search?q=4%2C8%2C12%2C7%2C19%2C6%2C25%2C5&language=english&go=Search

So, it appears that this sequence may very well be just this:

4 8 12 
    12 7 19 
         19 6 25
              25 5 30
                   30 4 34

... Which means that it would start on the left side with -5 9 4, and continue on the right like this:

                             34 3 37
                                  37 2 39
                                       39 1 40
                                            40 0 40

Writing it this way, it would be a finite sequence symbolically written with a giant Sigma symbol, but I'll do it in APL-style Pseudocode here:
x=4
for (i=8; i>3; i++) {
y=x+i;
x=y;
}

[arethinn]

Really, all these things do is test how closely you think like the test's author.

No kidding.