It’s the Friday Puzzle!


coverPlease do NOT post your answer, but do say if you think you have solved the puzzle and how long it took. Solution on Monday.

A boat is at anchor.  There is a rope ladder hanging over the side of the boat, and the rungs of the ladder are a foot apart.  The sea is rising at a rate of 15 inches per hour.  After 6 hours, how much of the rope ladder will remain above the water, assuming that 10 feet of the ladder was above the water when the tide began to rise?
I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.

55 comments on “It’s the Friday Puzzle!

  1. Ruth Slavid says:

    I think I have it right – about 3 seconds.

  2. Simon Taylor says:

    Took as long as it took to read. Nice one.

  3. Harish says:

    Oh c’mon Richard, after all tricky calculations lately.. well, tricky indeed. Well played.

  4. DiscoveredJoys says:

    Ha! Trivial.

  5. Baker's Dozen says:

    For the purposes of this puzzle we should assume that

    1) The anchor is taut holding the boat at the same distance from the bottom;

    2) the rising sea cannot unhook the anchor or snap, letting the boat drift away.

    Otherwise the results could be confusing.

    • TBH says:

      I think you may have missed the point there, fella.

    • Baker's Dozen says:

      It’ll be interesting to see if this is the confusion.

    • mikekoz68 says:

      I think you should read TBH’s comment again…

    • Topher says:

      I’ll play along with you Baker’s Dozen.

      3) We’re told that when the tide began to rise the distance was 10 ft, but we’re not told that the six hours starts when the tide began to rise.

      4) It also doesn’t explicitly state that the tide continues to rise for the entire six hours.

      Looks like it’s impossible to get the answer through calculations. 😉

    • Baker's Dozen says:

      Yes you’re right. I’m looking forward to all the different possible answers to the question on Monday. Maybe this is more philosophical ?

    • Ken Haley says:

      I don’t think anyone who cared about his boat would anchor it that tightly, knowing the tide would be rising.

    • Mervulon says:

      Perhaps it must be pointed out that taut line or not, no anchor is heavy enough to sink the boat that carries it.

  6. Phil Kent says:

    This seems to bloody obvious… I must have it wrong

  7. Anne Elk says:

    Puzzle Nostalgia! I remember this one from school. But it’s a good one.

  8. Anonymous says:

    Yes also got it. Had the answer before I got to the question. Could see where that was going. Nice though !

  9. Steve Jones says:

    I’m tempted to shout Eureka…

  10. Danielle Kennedy says:

    Trivial question.

    Unless the anchor rope is taut and vertical before the tide starts rising, but then you’ve got a problem.

  11. Tom Cook says:

    Zero seconds

  12. Solved it before I had completely finished reading it (a rather rare occurrence for me).

  13. Theo van Trier says:

    This one I have seen before, but then with the water rising at 10 inches per hour.
    Makes all the difference. 🙂

  14. Andy Jackson says:

    About 2 seconds :0)

  15. Jon says:

    Seriously this was about zero seconds.

  16. The Masked Twit says:

    How long is a piece of string?

  17. Anonymous says:

    I’ve seen this one before, but it still made me smile.

  18. VicinCA says:

    About 3 seconds.

  19. mittfh says:

    Assuming there’s some slack in the anchor chain and the boat’s seaworthy (i.e. nobody punches holes in the bottom), I’m fairly sure that I’ve calculated the most probable answer without needing to resort to pen and paper or Excel 🙂

  20. Colin Adams says:

    got it straight away. At least I think I do 🙂

  21. ctj says:

    this is much better than the one about carving a heart in a tree.

  22. mightyhero says:

    Too easy.

  23. JeffJo says:

    -3 seconds (got it halfway thru the third sentence). But the more interesting question is, where will the boat be after 12 hours?

  24. Miss Chili says:

    Assuming that the lead to the anchor isn’t taut, I got it straight away. Without that assumption, I got it at the same time. Guess we’ll see which ass I’ve made on Monday! 😀

  25. Edgar says:

    I also solved it as soon as I finished reading it.

  26. Jon says:

    ” The sea is rising at a rate of 15 inches per hour. After 6 hours”

    That’s not how tides work.

  27. SilverMarc says:

    I was asked this one about 50 years ago, but I got it WRONG! Fun puzzle!

  28. Dharmaruci says:

    many posters here think they have been clever and made the no-math answer to this puzz. but what if the boat is at anchor in a low cave, or under a pier? the ans then is much different.

    • ctj says:

      most of the fun of reading the comments on monday is seeing all of the ways that Richard poorly phrased his puzzle, or all of the plausible ways that he (could have) got the answer wrong.

    • JeffJo says:

      And what if it isn’t in the sea at all? Or already sunk in three feet of water?

      It’s a puzzle. You have to assume that all the information needed to solve it is given to you.

  29. Fotoflex says:

    If the boat is for anchor at the Waddenzee, after 6 hours all water is gone……

  30. veli says:

    Sneaky Little Hobbitses, Wicked, Tricksy, False!

  31. James Bailey says:

    Started down the wrong road – then the brain kicked in, so probably about a minute.

    Might have been more challenging if it were this rope ladder:

  32. Guy says:

    5 hours to solve this one.

  33. Physicalist says:

    Had it by the time I finished reading.

  34. hanson says:

    If the boat is for anchor at the Waddenzee, after 6 hours all water is gone……and the boet is a light weight so it most float .so how much of the rope ladder will remain above the water , the ladder remain is 9feet

  35. dgwolf says:

    So many of you seem to be over thinking this …

  36. john jahanpour-burke says:

    Got It In 10 Seconds. It Is So Easy.I Like This Trick Question. I Told It To All My Family Members And My Sister Got It First.

  37. john jahanpour-burke says:

    Wouldn’t The Ladder Float Also?

  38. dayuntoday says:

    Duh. Got it before I was done reading. As will anyone who’s ever spent any time on a boat.

  39. issahamati says:

    for ever because both of them will rising .

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