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Suppose you draw three marbles from the box, then there is a possibility that all three are of different colors (though it is always possible that the first two drawn are of the same color, but here we are to find the number of balls to be drawn such that we are sure that at least two among them are of the same color).
Now, if you draw a fourth marble from the box, then it has to be one of a 'Green', a 'Yellow' or a 'Blue' marble, which implies that now we are sure to have at least two marbles of the same color.
Therefore, the answer is: Four marbles. |
