A market survey shows that 30% of the population used Brand X laundry detergent last year, 8% of the population gave up doing its laundry last year, and 3% of the population used Brand X and then gave up doing laundry last year. Are the events of using Brand X and giving up doing laundry independent? Is a user of Brand X detergent more or less likely to give up doing laundry than a randomly chosen person?   First, we need to test whether the two events are independent. Use X to denote the event described by "A person used Brand X," and G to describe the event "A person gave up doing laundry." Recall that the two events are independent if and only if the probability of  G ∩ X  is equal to the product of the probabilities of X and of G. That is, if and only if  P(G ∩ X) = P(G) · P(X). To answer the question, calculate P(G), P(X), and  P(G ∩ X)  and then compare  P(G ∩ X)  to  P(G) · P(X). Because 8% of the population gave up doing laundry, the probability that someone quit doing laundry is  P(G) = 0.08. Similarly, 30% of the population used Brand X, so the probability that someone was a Brand X user is  P(X) =  0.3 Furthermore, 3% of the population used Brand X and then gave up doing laundry, so the probability that someone was initially a Brand X user and then quit doing laundry is  P(G ∩ X) =

A First Course in Probability (10th Edition)
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ISBN:9780134753119
Author:Sheldon Ross
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Chapter1: Combinatorial Analysis
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A market survey shows that 30% of the population used Brand X laundry detergent last year, 8% of the population gave up doing its laundry last year, and 3% of the population used Brand X and then gave up doing laundry last year. Are the events of using Brand X and giving up doing laundry independent? Is a user of Brand X detergent more or less likely to give up doing laundry than a randomly chosen person?
 
First, we need to test whether the two events are independent.
Use X to denote the event described by "A person used Brand X," and G to describe the event "A person gave up doing laundry."
Recall that the two events are independent if and only if the probability of 
G ∩ X
 is equal to the product of the probabilities of X and of G. That is, if and only if 
P(G ∩ X) = P(G) · P(X).
To answer the question, calculate P(G), P(X), and 
P(G ∩ X)
 and then compare 
P(G ∩ X)
 to 
P(G) · P(X).
Because 8% of the population gave up doing laundry, the probability that someone quit doing laundry is 
P(G) = 0.08.
Similarly, 30% of the population used Brand X, so the probability that someone was a Brand X user is 
P(X) =  0.3
Furthermore, 3% of the population used Brand X and then gave up doing laundry, so the probability that someone was initially a Brand X user and then quit doing laundry is 
P(G ∩ X) =
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