Suppose that a and b are events with probabilities p(a) = 3/4 and p(b) = 1/3. (a) (8 points) what is the largest p(a ∩ b) can be? what is the smallest it can be? give examples to show that both extremes for p(a ∩ b) are possible. (b) (8 points) what is the largest p(a ∪ b) can be? what is the smallest it can be? give examples to show that both extremes for p(a ∪ b) are possible

  (a) max P(A∩B) = 1/3; min P(A∩B) = 1/12

  (b) max P(A∪B) = 1; min P(A∪B) = 3/4

Step-by-step explanation:

Let the universal set be the numbers 1–12, U = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}, each with probability 1/12.

Let event A be any of the numbers 1–9, {1, 2, 3, 4, 5, 6, 7, 8, 9}. If a number is chosen at random from U, the probability of event A is 9/12 = 3/4.

a1) Let event B be any of the numbers 1–4, {1, 2, 3, 4}. If a number is chosen at random from U, the probability of event B is 4/12 = 1/3.

The set A∩B is the numbers 1–4, {1, 2, 3, 4}, so the probability of that event is also 4/12 = 1/3.

In general the maximum value of P(A∩B) will be min(P(A), P(B)). Here, that is min(3/4, 1/3) = 1/3.

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a2) Let event B be any of the numbers 9–12, {9, 10, 11, 12}. If a number is chosen at random from U, the probability of event B is 4/12 = 1/3. The set A∩B is the number {9}, so the probability of that event is 1/12.

In general, the minimum value of P(A∩B) is max(0, P(A) +P(B) -1). Here, that is max(0, 3/4 +1/3 -1) = 1/12.

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b1) Let event B be defined as in (a2), the numbers 9–12. Then A∪B is the set {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}, which is equal to the universal set, U. That is, the probability of event A∪B when drawing a number from U is 1.

In general, the maximum value of P(A∪B) is min(1, P(A)+P(B)). Here, that is min(1, 3/4+1/3) = 1.

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b2) Let event B be defined as in (a1), the numbers 1–4. Then A∪B is the set {1, 2, 3, 4, 5, 6, 7, 8, 9}. If a number is chosen at random from U, the probability of event A∪B is 9/12 = 3/4.

In general, the minimum value of P(A∪B) is max(P(A), P(B)). Here, that is max(3/4, 1/3) = 3/4.

an advantage of the standard deviation is that it increases as the dispersion of the data increases. e. the interquartile range is preferred when the data are not skewed or no have outliers. an advantage of the standard deviation is that it uses all the observations in its computation.

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