School-Safe Puzzle Games

Contest! Lateral Thinking Number Puzzle

lift the golden cup

Big Thanks to Bobo The Bear for sending in this very nice lateral thinking puzzle he created:

The following two-digit numbers all have something in common:

11, 15, 20, 40, 55, 60, 90

There is only one other two-digit number that shares the same feature. What is that number, and what do they all have in common? The 1st  reader that figures this out will win a RUNES puzzle package (not too late to buy for a great Christmas gift!). The 2rd and 3rd to figure it out will get the Smartkit PDF puzzle book.

Will announce winners (and all who can figure it out!) before the week is over. If you can figure it out, enter answer below in comment section.

20 Comments to “Contest! Lateral Thinking Number Puzzle”

  1. aaronlau | Profile

    11, 15, 20, 40, 51, 55, 60, 90
    XI, XV, XX, XL, LI, LV, LX, XC
    Roman numerical in ascending order.


  2. aaronlau | Profile

    Restriction of 2 digit for numerical and 2 alphabets for roman numerical.

  3. Falwan | Profile

    10 !

    90 ÷ 15 = 6

    55 ÷ 11 = 5

    60 ÷ 20 = 3

    40 ÷ ? = 4

    ? = 10

    that’s the pattern I found.

    Thank You Bobo…

  4. RK | Founder | Profile

    The answers for ‘Measuring Hobbiton’ have been unmasked

  5. jamesbuc | Profile

    They have two digits both when expressed in decimal and as Roman Numerals:


    51 (LI) is the only other number that shares this property.

  6. suineg | PUZZLE MASTER | Profile

    The number is 51.

    This are the numbers written in Roman numerals in ascending order:

  7. dmp12 | Profile

    The answer is 51. It is the only other two-digit number that is made up of two Roman Numerals.

    11 = XI
    15 = XV
    20 = XX
    40 = XL
    51 = LI
    55 = LV
    60 = LX
    90 = XC

  8. Blusummers13 | Profile

    The last number is 51. They are all two-digit numbers with two-digit roman numerals as well.

  9. hex | PUZZLE MASTER | Profile

    These are the 2 only digit numbers that can be written in Roman numerals using 2 digits

  10. hex | PUZZLE MASTER | Profile

    minor typo:

  11. diegote | Profile

    The other number is 51. All numbers can be represented as roman numbers with 2 symbols.

    11 – XI
    15 – XV
    20 – XX
    40 – XL
    55 – LV
    60 – XL
    90 – XC
    51 – LI

  12. abcbcdcdef | Profile

    or I should say LI?
    the numbers in roman numerals are all represented with two letters only, that is:
    XI, XV, XX, XL, LV, LX, XC
    the only one left that can be represented in two roman numerals is LI–51

  13. RK | Founder | Profile

    Congratulations to all of you that figured it out. Didn’t think many would get this one!

    As you can see above, the 1st 3 to get it right:


    shoot me an email and will send out the prizes

    Wanted to get the 3rd puzzle box and Whoa Kitty up this am, but ran short on time, sorry about that. Still might be able to get them up a bit later though…

  14. Bobo The Bear | PUZZLE MASTER | Profile

    Well done to those of you who got it. I really didn’t know if it would be too easy, too tough, or somewhere in between. I hope you all enjoyed the puzzle.

  15. hex | PUZZLE MASTER | Profile

    Looks like by the time I first saw the puzzle, 6 correct answers had already been submitted 8-)

    I’ll have to settle with a pat on the back

    RK, when are you going to include a link on puzzle pages to the emoticons page so we can easily express our funny emotions correctly?

  16. RK | Founder | Profile

    @Hex- early bird cathes the worm ;)
    But, since you really helped me out with the site hacking issue, if you’d like the RUNES or PDF, shoot me an email and I’ll get one out to you this weekend :)

    emoticons coming soon, I promise!

  17. RK | Founder | Profile

    And Thanks again Bobo for contributing the puzzle

  18. hex | PUZZLE MASTER | Profile

    @RK, That’s very kind of you. But allow me to choose neither, especially that I didn’t do a big deal in the site hacking issue.

    On the other hand, I’ll be on the watch for the emoticons.

  19. wpamensa | Profile

    51 = LI

Enter an Answer/Comment/Reply

To comment log in or register for a free Smartkit account.

Recent Comments Sign In