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Discrete Math

Two student council representatives are chosen at random from a group of 7 girls and 3 boys. Let G denote the distribution over the number of girls chosen.
a. What is the range of G?
b. Give the distribution over the random variable G.

User Anestis
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Answer:

Explanation:

a. The range of G is the set of possible values that G can take. G represents the distribution over the number of girls chosen, so G can take any value between 0 and 2, inclusive. That is, the range of G is {0, 1, 2}.

b. To give the distribution over the random variable G, we need to determine the probability of each possible value of G.

Let's consider each possible value of G in turn:

If no girls are chosen (G=0), then both representatives must be boys. The probability of choosing a boy on the first draw is 3/10, and the probability of choosing another boy on the second draw is 2/9 (since there are only 2 boys left). Therefore, the probability of G=0 is (3/10) * (2/9) = 1/15.

If one girl is chosen (G=1), then one representative must be a girl and the other must be a boy. There are two ways this can happen: either the girl is chosen first and then the boy, or the boy is chosen first and then the girl. The probability of choosing a girl on the first draw is 7/10, and the probability of choosing a boy on the second draw is 3/9 (since there are 3 boys left). The probability of choosing a boy on the first draw is 3/10, and the probability of choosing a girl on the second draw is 7/9 (since there are 7 girls left). Therefore, the probability of G=1 is (7/10) * (3/9) + (3/10) * (7/9) = 14/45.

If two girls are chosen (G=2), then both representatives must be girls. The probability of choosing a girl on the first draw is 7/10, and the probability of choosing another girl on the second draw is 6/9 (since there are 6 girls left). Therefore, the probability of G=2 is (7/10) * (6/9) = 7/15.

Therefore, the distribution over the random variable G is:

G=0 with probability 1/15

G=1 with probability 14/45

G=2 with probability 7/15

User Katinka
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