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The Classic Weights & Scale
You have 8 lead marbles, one of which is heavier than the rest. What is the minimum amount of “weightings” (i.e. with a see-saw scale) you need to do to guarantee finding the odd one out?
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Discussion
I thought that the answer was 3.(log-2 of 8)
@sysop073:
the scale is not binary, the scale has 3 states, less heavy, more heavy and equal
therefore the answer is ceil ( log_base3( number of marbles) ). i think
could also do this with 9 balls and have the same answer
Here is another puzzle, much harder but can be done. Given 11 billiard balls all of which weigh the same and a 12th that is either lighter or heavier than the others, determine in a max of 3 uses of the scale which is the odd ball and if it is lighter or heavier than the others. Same type of scale.
Google:
“12 billiard balls” weigh
for numerous solutions
Difficulty
Currently: Moderate (5.0)