Sandy Wood
Brain Game: Math Monday II (or is it III?)
by Sandy Wood - March 23, 2009 - 7:30 AM

bloghead_braingames.jpg

Math Monday makes its return. This puzzle is worth some effort, because even when you figure out what the answer should be, you have to figure out what the answer is. I hope you find it challenging. (For what it’s worth, the Roman numerals in this post’s title are no hint whatsoever. Really.) Good luck!

What’s the next number in this sequence?

1, 0, 11, -12,… ?

Here is the SOLUTION.

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Comments (10)

  1. The link for the solution takes us to the Elite Eight answer.

    ED NOTE: All fixed, KJ!

    posted by KJ on 3-23-2009 at 8:19 am

  2. Maybe it’s a stretch, but I came up with 46 – if you just take the differences of the terms, you get -1, +11, -23, which to me looked like the beginning of the Fibonacci sequence, so I went with +58 for the next difference, and therefore the next term would be +46.

    posted by Jeremy on 3-23-2009 at 8:40 am

  3. Jeremy, not a stretch at all. The whole point of the Brain Game is not even whether you get the right answer or not, but to keep the old noggin oiled. Sometimes they’re tougher and more obscure (like today’s puzzle) and sometimes they jump right out at you.

    I’ve spent my whole life trying to look at things from different angles… to me, that’s what learning is all about.

    (Sorry that sounds like a bad commencement speech!)

    posted by Sandy Wood on 3-23-2009 at 9:27 am

  4. My answer was 26.

    Think of it as a pyramid of differences, and it just so happens my first number is 1 (cause really, everything starts with 1!). Odd rows you subtract, even rows you add.

    1

    Now I have 1 row, with the sum of the numbers equaling 1. That gives me 11 (1 row totaling 1).

    1
    11

    Now I have 2 rows, and the numbers total 3. Which gives me 23 (2 rows totaling 3).

    1
    11
    23

    Now I’ve got 3 rows, numbers totaling 8. Giving me 38.

    1
    11
    23
    38

    So my sequence is 1, 0, 11, -12.
    Starting with 1, I add -1 (negative b/c 1st row), giving me 0. Then add 11 (positive, row 2), giving me 11. Then add -23 (row 3), giving me -12. Then add 38 (row 4), giving me 26.

    Kind of round about, but I guess it’s just how my mind works :)

    posted by Ellen on 3-23-2009 at 10:47 am

  5. Come to think of it, I like Jeremy’s answer better :)

    posted by Ellen on 3-23-2009 at 10:49 am

  6. I like Ellen’s answer!

    posted by Brooke on 3-23-2009 at 11:55 am

  7. My answer was 111

    But now I see I should have worked it out on paper.

    (I still don’t think I would have gotten the right answer, but I would have seen mine was wrong!)

    oh well!

    posted by Meri on 3-23-2009 at 11:59 am

  8. I got 101:

    take the series: 0, -1, 2, -3, 4
    convert it to binary: 0, -1, 10, -11, 100
    pretend those binary numbers are decimal and then add 1 to the absolute value of each: 1, 0, 11, -12, 101

    posted by John on 3-23-2009 at 11:17 pm

  9. oops. that doesn’t actually work

    posted by John on 3-23-2009 at 11:26 pm

  10. I can’t believe it… we went all day without someone pointing out that this was “numbers, not math.”

    Heh!

    posted by Sandy Wood on 3-24-2009 at 1:15 am

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