1. Standard memberPBE6
    Bananarama
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    01 Nov '06 20:001 edit
    Not sure if this one has been posted here or not, so here goes:

    You are given 2 identical glass balls with the task of determining their breaking strength (you can assume that breaking strengths for each ball are equal). To do this, you have to drop the balls from different floors in a 100-story building and see if they break (again, you can assume that the breaking strength is 100 stories or less). Once a glass ball is broken, it cannot be used again. What is the minimum number of drops you need to make to determine the breaking strength?

    Hint: It's much less than 100.
  2. Joined
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    01 Nov '06 20:23
    Originally posted by PBE6
    Not sure if this one has been posted here or not, so here goes:

    You are given 2 identical glass balls with the task of determining their breaking strength (you can assume that breaking strengths for each ball are equal). To do this, you have to drop the balls from different floors in a 100-story building and see if they break (again, you can assume that the ...[text shortened]... of drops you need to make to determine the breaking strength?

    Hint: It's much less than 100.
    1
  3. Joined
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    01 Nov '06 20:25
    18
  4. Standard memberPBE6
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    01 Nov '06 20:25
    Originally posted by mlprior
    1
    No.
  5. Standard memberPBE6
    Bananarama
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    01 Nov '06 20:25
    Originally posted by Diapason
    18
    Close, but it's less than that.
  6. Joined
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    01 Nov '06 20:41
    14
  7. Standard memberPBE6
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    01 Nov '06 21:00
    Originally posted by Diapason
    14
    We have a weiner! Care to explain your solution?
  8. Joined
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    01 Nov '06 21:05
    Originally posted by PBE6
    We have a weiner! Care to explain your solution?
    Start dropping at 14. If it breaks try the 13 floors up to 14. Total drops = 14.
    Next drop at 14+13=27. If it breaks try the 12 floors between 14 and 27. Total drops = 14.
    Next drop at 14+13+12 etc.

    Nice puzzle - thanks for posting it.
  9. Standard memberPBE6
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    01 Nov '06 21:29
    Originally posted by Diapason
    Start dropping at 14. If it breaks try the 13 floors up to 14. Total drops = 14.
    Next drop at 14+13=27. If it breaks try the 12 floors between 14 and 27. Total drops = 14.
    Next drop at 14+13+12 etc.

    Nice puzzle - thanks for posting it.
    Quite correct. Good answer! For the others, you can try starting on the 13th floor or less, but you find that you can't get up to the 100th floor without making extra drops so you can't guarantee the breaking strength.
  10. Joined
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    01 Nov '06 22:10
    I found it too 😛
    I figured out that way of moving up by one number less each time and then just started adding up till i was at hundred 😛
    1+2+3+...+13=91
    1+2+3+...+14=105
    So 14 has to be the correct answer
  11. Edmonton, Alberta
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    02 Nov '06 03:58
    What?

    2 Balls you got.

    You drop ball 1 from 14th floor it breaks = 1 drop.

    You take ball 2 drop it from 13th floor it breas = 2 drops.

    You have no more balls left and you still don't know if the breaking strenght is 13 floors or less then that.
  12. Standard memberXanthosNZ
    Cancerous Bus Crash
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    02 Nov '06 04:55
    Originally posted by RahimK
    What?

    2 Balls you got.

    You drop ball 1 from 14th floor it breaks = 1 drop.

    You take ball 2 drop it from 13th floor it breas = 2 drops.

    You have no more balls left and you still don't know if the breaking strenght is 13 floors or less then that.
    Say you drop the first ball from the 14th and it breaks. Therefore the breaking point is less than 13. So now you drop the ball from each floor in turn starting at floor 1. That will take at most 13 drops totalling 14 drops.

    If the first ball doesn't break when dropped from the 14th floor then you drop it from the 27th. If it breaks on that drop then you drop from the 15th -26th in order to find the breaking point. That will take 12 drops totalling 14 drops.

    And so on with drops being from the 39th, 50th, 60th, 69th, 78th, 85th, 91st, 96th and then 100th. Each of these works like above.

    The maximum drops will be 14.
  13. Standard memberuzless
    The So Fist
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    02 Nov '06 21:23
    Originally posted by Diapason
    Start dropping at 14. If it breaks try the 13 floors up to 14. Total drops = 14.
    Next drop at 14+13=27. If it breaks try the 12 floors between 14 and 27. Total drops = 14.
    Next drop at 14+13+12 etc.

    Nice puzzle - thanks for posting it.
    you can't start at floor 1...the 1st floor is not above the ground.
  14. Joined
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    02 Nov '06 22:54
    Originally posted by uzless
    you can't start at floor 1...the 1st floor is not above the ground.
    It is here in England!
    We start at the Ground Floor. The next floor up is called the 1st floor.
  15. Waynesboro, PA
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    02 Nov '06 23:06
    you are on a path that eventually leads to a fork in the road. One way......whatever you may dream of (the right way)....and the other way.....your worst night mare (the wrong way). two brothers.....one always lies one always tells the truth (thos are the conditions under every circumstance) one question to find out the right way.....what question do you ask? I know this is more of a riddle than a puzzle for those who like to be politically correct but whatever 🙂
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