About M&Ms and probability

A bowl contains a number of m&m’s, with equal numbers of each color. Adding 20 m&m’s of a new color to the bowl would not change the probability of drawing (without replacement) two m&m’s of the same color.

How many m&m’s are in the bowl before the extra m&m’s are added?

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This is under conditional probability

The formula is

P(B/A)= P(A and B)/P(A)

For the probability to remain the same after adding 20 m&m’s of a new color, then, the other colors must have been in groups of 20’s.

Thus, we can assume that there were 20 blue, 20 red and we added 20 green

The probability will thus be

P(B/A)= P(A and B)/P(A)

The total number of m&m’s in this case would be…