60 Comments

1. Steven Miller on November 9, 2012 at 1:37 am

   haha — there’s a better soln — sjm1 AT williams.edu

   
   
   
2. kylekotke on November 8, 2012 at 11:35 pm

   jump

   
   
   
3. Steven Miller on June 25, 2012 at 4:34 am

   Mike L: the math works, well done

   
   
   
4. Steven Miller on June 24, 2012 at 3:20 am

   NO — there’s no time like the present (sjm1 AT williams.edu)

   
   
   
5. Mike L. on June 23, 2012 at 11:19 pm

   Is it okay to wait until Winter when there is a frost and waltz on over using the boards to keep your feet from slipping?

   
   
   
6. Steven Miller on June 11, 2012 at 8:56 pm

   emailed hint //s

   
   
   
7. Irving on June 11, 2012 at 8:31 pm

   Been working on this for a while. Can you please email me the answer!!

   Thanks!

   
   
   
8. Steven Miller on June 9, 2012 at 3:54 am

   nope. //s

   
   
   
9. Chris on June 7, 2012 at 10:07 pm

   Depending on the depth of the water (assume 1 inch for our purposes), you can have your plank go from the water to the edge and step roughly 0.2 meters onto the plank and walk across.

   
   
   
10. Steven Miller on May 6, 2012 at 11:56 am

    Did I mention that we’re on Jupiter, with a very strong gravitational field? It’s all we can do to crawl…. :]

    
    
    
11. tom on May 5, 2012 at 10:25 pm

    can’t you just jump across it? its only 5 meters

    
    
    
12. Steven Miller on April 15, 2012 at 8:27 pm

    sure == just sent (sjm1 AT williams.edu)

    
    
    
13. Ann on April 15, 2012 at 9:48 am

    Hello, please would you send me a hint, all my ideas seem physicaly unimplementable

    
    
    
14. Steven Miller on April 14, 2012 at 3:52 am

    sure, done //s

    
    
    
15. Rosa on April 13, 2012 at 7:37 pm

    I’m having a hard time with this riddle. Can you please email me a hint?

    
    
    
16. Steven Miller on April 3, 2012 at 1:43 pm

    nope — that won’t be secure enough to walk over….

    
    
    
17. Banani on April 3, 2012 at 12:27 pm

    place them so they lean on each other above the mote and pass over them ?

    
    
    
18. Steven Miller on April 1, 2012 at 7:26 pm

    I’ll send hints first. //s

    
    
    
19. E on April 1, 2012 at 6:45 pm

    Can I have the solution to this and Sumthing’s Up?

    
    
    
20. Steven Miller on March 14, 2012 at 1:12 am

    correct, those don’t matter //s

    
    
    
21. Jakwanul Safin on March 14, 2012 at 12:39 am

    it didn’t specify the thickness or width of the boards and the height of the moat

    
    
    
22. Steven Miller on March 9, 2012 at 2:55 am

    you’re actually very heavy, but these are sturdy boards. nice attempt, but there is a clean ‘math’ soln

    
    
    
23. StarFox on March 9, 2012 at 2:43 am

    yes…but no pole, I ‘d say, stand on one, assume you are ultra light, and use the other to paddle across

    
    
    
24. Anonymous on February 19, 2012 at 1:53 am

    pole jump the moat.

    
    
    
25. Steven Miller on February 18, 2012 at 9:50 pm

    Hi — if you want to chat about these riddles, especially putting these into a classroom setting, feel free to email me at sjm1 AT williams.edu

    
    
    
26. dede on February 18, 2012 at 5:32 pm

    hi

    
    
    
27. Steven Miller on February 12, 2012 at 2:42 am

    imagine you have two circles, with the outer having a radius that’s 5 meters longer than the smaller circle. the area b/w is the moat. does this help?

    
    
    
28. The PuzzleSolver on February 11, 2012 at 1:48 pm

    Could you please explain this question more clearly?

    
    
    
29. Steven Miller on February 8, 2012 at 1:48 pm

    sure //s

    
    
    
30. Steven Miller on February 8, 2012 at 2:00 am

    say it’s two inches wide, but VERY sturdy.

    
    
    
31. John Thompson on February 8, 2012 at 12:15 am

    I’ve been trying this for a while and I’ve read all of the comments but they just confuse me. Can you send me a hint please?
    Thanks

    
    
    
32. ed on February 7, 2012 at 9:47 pm

    How wide is the plank. If it is a square then this is easy to solve.

    
    
    
33. Steven Miller on February 7, 2012 at 5:45 pm

    I’ll send a hint first. //s

    
    
    
34. Dimitri on February 7, 2012 at 4:40 pm

    i cant emagine the whole picture, please tell me the answer.

    
    
    
35. Steven Miller on January 26, 2012 at 2:20 pm

    sure, I’ll email a hint. Hope the crew is enjoying them. //s

    
    
    
36. Matt on January 26, 2012 at 1:48 pm

    I’m obviously missing something here. Even after reading all of the comments, I’m even more confused. It pains me to ask but can i get a hint please?

    These are cool by the way, i post them in our jobsite trailer everyday for the crew to try and solve.

    
    
    
37. Steven Miller on November 18, 2011 at 8:38 pm

    Absolutely, will do

    
    
    
38. Darlane Evans on November 18, 2011 at 6:08 pm

    Hi, Steve! Love your site. I have several classes of 4th graders working on some of your problems, including this one. Can their teacher or myself email their solutions to you so they can check their answers?

    
    
    
39. Steven Miller on October 19, 2011 at 12:59 pm

    nope, there is a simple, geometrical soln

    
    
    
40. William Fox on October 19, 2011 at 6:01 am

    Polevault?

    
    
    
41. Steven Miller on October 17, 2011 at 2:43 am

    picture a circle and then a larger circle, with say a 5 meter separation.

    
    
    
42. Linh on October 17, 2011 at 2:34 am

    Im not picturing this. It’d be easier to understand if there were a picture 🙁

    
    
    
43. Steven Miller on October 9, 2011 at 1:42 am

    ah, but will those support the weight? Andre the Giant’s bigger brother is coming….

    
    
    
44. ME on October 8, 2011 at 5:14 pm

    or you could do it the non mathy way and steeple the planks

    
    
    
45. Steven Miller on August 18, 2011 at 6:03 pm

    But that won’t have you CROSS it.

    
    
    
46. Anonymous on August 18, 2011 at 6:01 pm

    just walk around tha moat as the question never said how long it was

    
    
    
47. Steven Miller on August 18, 2011 at 1:59 am

    To: marckorevaar1@

    You are correct, but made an algebra error on lengths.

    
    
    
48. Marc on August 16, 2011 at 6:09 pm

    Hi Steve,
    If placing the planks in the corner of the moat (the 1st plank at 45 degrees to either edge and the 2nd plank from the center of the 1st plank to the corner of the castle side of the moat). My problem is that the length needed to cross is: sqrt(50)=+/-7.07 which is larger than the length obtained by the 2 boards: 4.5 + 4.5/2= 6.75.
    Could you give me a hint as i think i miss something.
    Cheers, Marc
    PS: thanks for all the riddles

    
    
    
49. Steven Miller on July 27, 2011 at 3:41 am

    Sure, sent along.

    
    
    
50. aashutoshh on July 26, 2011 at 7:26 pm

    hint plssss…

    
    
    
51. Steven Miller on July 6, 2011 at 2:38 am

    Sure — will email you. //s

    
    
    
52. brenda on July 6, 2011 at 2:32 am

    i dont get this…can u give me a hint?

    
    
    
53. Steven Miller on June 1, 2011 at 7:03 pm

    This seems like you’re solving the problem 3-dimensionally and building upwards. You don’t need to do this.

    
    
    
54. Guy on June 1, 2011 at 6:29 am

    Is the answer you place the two boards at 45 degree angles over the five meter moat, with by just leaning over the .5 meter to place the first plank over on the other side, then using your second plank to lever it into place, so that the hypotenuse would be the square root of two times 4.5, which is about 6.36, to cover the 5 meter moat-span? And then just… applying force evenly as you walk against the point where the two planks meet so it won’t fall over. Or is this a lot more complicated than that, and also if that’s even possible?

    
    
    
55. Steven Miller on May 11, 2011 at 8:48 pm

    Sure, just emailed you.

    
    
    
56. Jake on May 11, 2011 at 3:31 pm

    I end up needing my second board to be 4.82 meters 😉 can you give another hint?

    
    
    
57. Steven Miller on May 3, 2011 at 1:37 am

    It’s so hard to judge these riddles. So many of them depend on whether or not you see the right way to look at them quickly (in which case they’re easy as often there is an elegant solution), or not.

    
    
    
58. ACE on May 2, 2011 at 8:04 pm

    I think this one should be put in the easy category 🙂

    
    
    
59. Steven Miller on April 6, 2011 at 1:32 pm

    Yes — the moat is rectangular (or perhaps a square — I forget how the problem is phrased right now).

    
    
    
60. Jay on March 29, 2011 at 8:30 pm

    I suspect that the riddle should state that the moat is rectangular.