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Horrordee
Soderator
Posts: 8868
Location: England
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 Posted: Tue, 1st Mar 2005 23:20 Post subject: My eight marbles |
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OK, i have a question for you all. You are given eight marbles, all of which look the same and are undistiguishable. Now, one of these marbles is heavier than the other seven, although you don't know what one. You have a pair of two sided weighing scales on which you can weigh one side against another to see which side is heavier, or if they are of the same weight.
Now, you can find the heaviest marble in three steps by first dividing the 8 in 2, and weighing the two sets, discarding the lightest set of four and then splitting the heavier four into two groups of two. You do the same again and discard to lightest and finally you are left with two marbles, one being the heaviest, using the scales for a third time allows you to find the heaver marble, thus you've found the heavy marble in two three steps.
Now, it is actually possible to find the heaviest marble in just two steps, can you work this out?
WARNING TO EVERYBODY, THE POSTS BELOW THIS ONE ARE LIKELY TO CONTAIN THE ANSWER - IN FACT, IF NO ONE GETS IT IN A HOUR I'LL POST THE ANSWER, SO DON'T LOOK DOWN UNLESS YOU WANT TO.
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spankie
VIP Member
Posts: 2958
Location: Belgium
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| Posted: Tue, 1st Mar 2005 23:45 Post subject: |
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divide in 3 3 2 a b c / d e f /g h
put the a b c d e f on the weighing scale
if balanced, weigh the other 2 (g h), the balance will solve your problem
if not, take 2 of the 3 heaviest (e.g. b c)
if balanced, the third one is the heavy one (a)
if not balanced=>solved (b or c)
only works if you know one is heavier or you know one is lighter, one has a different mass isnt enough
2 minutes of thinking, we had something similar in math(statistics, for which i got an A(13+) today  ), where you had to divide into 5&3, didnt work here, 332 did
love those things, gimme more 
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Esel_Gesi
VIP Member
Posts: 3802
Location: Chicago
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| Posted: Wed, 2nd Mar 2005 00:05 Post subject: |
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