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You are given a bag of marbles, all of which are of the same shape and appearance. All the marbles are also of?
You are given a bag of marbles, all of which are of the same shape and appearance. All the marbles are also of the same weight except one of which is heavier than the rest. You are to use a balance to make exactly two weighings to pick out the heavier marble from the rest of the marbles. Describe clearly how you can do it. How would your answer differ if the bag contains exactly 6, 7, 8 or 9 marbles.
3 Answers
- MorningfoxLv 71 decade agoFavourite answer
If there are 6 marbles, I do it like this.
(1) weigh 2 against 2.
If one side is heavier, then you know the heavy one is in a group of two.
If they balance, then you know the heavy one is in the group (of two) that you left out.
(2) In the group of two that includes the heavy marble, weight them against each other.
If there are 7, then
(1) weigh 3 against 3
If one side is heavy, then you have a group of 3 that includes the heavy one.
If they balance, then the heavy one is the marble left out
(2) If it comes down to a group of 3, then weigh 1 against 1.
If there are 8, then it's just like 7. Except that you leave 2 out of the first weighting.
If there are 9, then you leave 3 out of the first weighting.
- Anonymous1 decade ago
Make a large bowl of Jello or gelatin. Level off the top so it is perfectly level. Now build a platform a fixed distance above the Jello, say 2 feet, and gently let each marble fall into the Jello side by side. The pull of Gravity will make the heavier marble sink deeper into the Jello.
