Derek and Mia place two green marbles and one yellow marble in a bag. Somebody picks a marble out of the bag without looking and records its color (G for green and Y for yellow). They replace the marble and then pick another marble. If the two marbles picked have the same color, Derek loses 1 point and Mia gains 1 point. If they are different colors, Mia loses 1 point and Derek gains 1 point. What is the expected value of the points for Derek and Mia?
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MathPhys MathPhys · Answer 1 · 2019-07-02T23:08:33+02:00

Step-by-step explanation:

With each draw, the probability of selecting a green marble is 2/3 and the probability of selecting a yellow marble is 1/3.

To pick two of the the same color, they can either pick green twice or yellow twice.

P = (2/3)(2/3) + (1/3)(1/3)

P = 5/9

To pick two different colors, they can either pick green first then yellow, or yellow first then green.

P = (2/3)(1/3) + (1/3)(2/3)

P = 4/9

Expected value for Derek is:

D = (5/9)(-1) + (4/9)(1)

D = -1/9

The expected value for Mia is:

M = (5/9)(1) + (4/9)(-1)

M = 1/9