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Heavy Marble

+12 votes
438 views
asked Mar 20, 2013 in Challenge / Quizzes by whizkid (66,440 points)
You have 8 marbles. They all look identical. However, one marble weighs more. A balance scale is available, but you you can just use it 2 times. How can you find the heavy marble?


3 Answers

+1 vote
answered Mar 23, 2013 by jamesaly (720 points)
 
Best answer
I figured this one out. First divide into 3 and 3 with 2 extra marbles on the side.

xxx xxx xx

Weigh the 2 sets of 3

xxx ---- xxx

If they weigh the same, just weight the extra 2 to find the heavy marble.

If one is heavier, remove the lighter set and select 2 from the heavier set.

x ---x  x

If they weigh the same, the heavy marble was the outside one. If one is heavier you also know the heavy marble.
0 votes
answered Mar 22, 2013 by mystic_beauty (18,110 points)

 


Make 2 groups of 4 marbles and weigh. The group that weighs more, split it into another 2 groups of 2 marbles and weigh. The group that weighs the most has the heavy marble, and to find which one, put one in either palm and feel which one is heavier...?

I don't really know...

-CraftyGirlJuJu
 
P.S. If you're wondering why there are two answers the same, I forgot to login, so..
commented Mar 22, 2013 by mathgeek36 (41,980 points)
Sometimes I do that too. After you log in, there's a button next to "flag"(I think), called "I wrote this". Then you can just click on that so that you don't have to write your answer again.
Hopefully this helps!
+2 votes
answered Mar 21, 2013 by anonymous
Make 2 groups of 4 marbles and weigh. The group that weighs more, split it into another 2 groups of 2 marbles and weigh. The group that weighs the most has the heavy marble, and to find which one, put one in either palm and feel which one is heavier...?

I don't really know...

-CraftyGirlJuJu

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