Doubt

Question

A bag contains 10 red marbles, 10 white marbles, and 10 blue marbles. What is the minimum no. of marbles you have to choose randomly from the bag to ensure that we get 4 marbles of same color?

Answer 1

10 marbles

In the worst case, you'll get different colored marbles in each draw.

Suppose in the first draw you get a red marble and in the second draw, a white marble and a red marble in the third draw. So now you have one marble of each color.

Repeating the above cycle thrice, you'll have 3 marbles of each red, white and blue color i.e. 9 marbles in all.

Now in the 10^th draw no matter what color marble you get, you'll have 4 marbles of same color.

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