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Bunuel
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Manali29
Hi

can you please explain where is that 2/5 coming from??

Out of 3 red ball, 1 is selected. For second selection, 2 red ball will be available. Please note : No replacement is mentioned in the question.
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Bag A contains 3 white and 3 red marbles. Bag B contains 6 white and 3 red marbles. One of the two bags will be chosen at random, and then two marbles will be drawn from that bag at random without replacement.

What is the probability that the two marbles drawn will be the same color?

Probability of selecting Bag A with 2 white marbles = 1/2*3C2/6C2 = 1/2 * 3/15 = 1/10
Probability of selecting Bag A with 2 red marbles = 1/2*3C2/6C2 = 1/2 * 3/15 = 1/10
Probability of selecting Bag B with 2 white marbles = 1/2*6C2/9C2 = 1/2 * 15/36 = 1/2 * 5/12 = 5/24
Probability of selecting Bag B with 2 red marbles = 1/2*3C2/9C2 = 1/2 * 3/36 = 1/24

The probability that the two marbles drawn will be the same color = 1/10 + 1/10 + 5/24 + 1/24 = 9/20

IMO C
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I'm confused about how taking 1/2 of each term would make sense
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kayarat600
I'm confused about how taking 1/2 of each term would make sense
\(\frac{1}{2}\) comes from the probability of selecting that particular bag.

Probability of selecting bag A = 1/2, now probability of selecting 2 red marbles from it = \(\frac{3C2}{6C2}\) => overall probability of this case = \(\frac{1}{2}*\frac{3C2}{6C2}\)

Similarly for all the other cases. Hope it helps.
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Yes it helps thank you
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