Find That Marble
There are 3 marbles of the same size but one marble is slightly heavier or lighter than the other two. Can you find which is that marble and if it is heavier or lighter? You can use a balance only two times.

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Solution

Suppose we have three marbles, A, B and C, such that one of them is slightly heavier or lighter than the other two. Let us first put marbles A and B in two different pans. We will get the following situations:

(1) If the two pans balance each other, then marble C is either heavier or lighter than the other two marbles. To check this, let us put marbles A and C in the two different pans. If the pan containing marble C goes down, then we can say that marble C is heavier than marbles A and B. If the pan containing marble A goes down, then we can say that marble C is lighter than marbles A and B.

(2) Suppose the two pans containing marbles A and B do not balance each other. Let the weight of marble A be less than that of marble B. Now, let us remove marble B from the pan and put marble C in its place. After this, let us compare the weights of marbles A and C. If the two pans balance each other, then we can say that marble B is heavier than marbles A and C. If the pan containing marble C goes down, then we can say that the weights of marbles B and C are equal and marble A is lighter than marbles B and C.

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Find That Marble There are 3 marbles of the same size but one marble is slightly heavier or lighter than the other two. Can you find which is that marble and if it is heavier or lighter? You can use a balance only two times.

Find That Marble
There are 3 marbles of the same size but one marble is slightly heavier or lighter than the other two. Can you find which is that marble and if it is heavier or lighter? You can use a balance only two times.