Thread: Random Puzzle

  1. #1

    Random Puzzle

    You need to boil an egg for 9 minutes, the water is already boiling in the saucepan.

    How can you measure exactly 9 minutes using a 4 minute sandglass timer and a 7 minute sandglass timer?

    Hint: You don't have to put the egg in as soon as you start the timer(s).
    Another hint: You might not need to use the above hint.

  2. #2
    Turn over both timers. After 4mins turn over the empty "4min" timer. After another 3 mins the "7min" timer is finished and the "4min" timer has 1min left in it. Put eggs in to boil at this point. Wait 1 min for the "4min" to finish then turn it over. 4mins later when its finished (now 5mins in to the eggs boiling) turn it again and wait the final 4 mins.

  3. #3
    Field Marshal
    Join Date
    Apr 2010
    Flip both timers over at the start. Flip the 4 minute one back over as soon as it ends (3m left on 7m timer).
    Once 7m timer ends flip it over again, 1m left on 4m timer. Flip 4m timer over again when it ends, 6m left on 7m timer.
    When the 4m timer ends, put the egg in - 2m left on 7m timer. Flip 7m timer over again when it ends, take egg out once it ends again, for a 9 minute boil.

  4. #4
    The Lightbringer Waaldo's Avatar
    Join Date
    Sep 2011
    Throw away the sandglass timers and use the digital one on the stove/microwave/cellphone/etc.
    These aren't the spoilers you're looking for.

    Move along.

    Quote Originally Posted by Blueobelisk View Post
    Now, Waaldo is prepared to look for this person like Prince Charming testing everyone to see just how bad their psychological disorder is if their foot fits in the glass slipper.

  5. #5
    That maybe a "correct" answer Waaldo but I'm asking for a solution in the traditional sense .

  6. #6
    Now the OP one has been solved...

    I was once asked to design the shortest puzzle possible, so here it is. (ps - very hard)


    Good luck

  7. #7
    The above answers are right but how do you measure the 9 minutes starting from as soon as you turn the timers over?!

    Can't do your puzzle schwarz, is it some kind of Rebus say what you see? One underscore?

  8. #8
    Quote Originally Posted by Twoddle View Post
    One underscore?
    You have the first bit done, two more steps and you are there

  9. #9
    For the original problem I will use fractions to depict the minutes of sand in the top and bottom of the two hour glasses.

    Add the egg and flip both glasses over and let the sand in the 4 minute time run fully, after 4 minutes the glasses are:
    0/4 and 3/4 - 4 minutes has passed
    Flip the 4 minute glass over and let them run until the 7 minute glass has fully emptied, which will be 3 minutes and the glasses are now:
    1/3 and 0/7 - 7 minutes has passed
    Flip both over and let them run until the 4 minute glass has fully emptied, which will be 1 minute and the glasses are now:
    0/4 and 6/1 - 8 minutes have passed
    Flip the 7 minute timer over and when it fully empties 1 more minute has passed for a total of 9 minutes.

  10. #10
    That's exactly how I did it RypPyr, well done.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts