4.17 Consider the following contingency table:

	B	B'
A	10	30
A'	25	35

What is the probability of

a. A I B?

b. A I B?

c. A I B?

d. Are events A and B independent?

4.18 If P(A and B) = 0.4 and P(B) = 0.8, find P(A I B).

4.19 If P(A) = 0.7, P(B) = 0.6, and A and B are independent, find P(A and B).

4.20 If P(A) = 0.3, P(B) = 0.4, and P(A and B) = 0.2, are A and B independent?

4.22 How will marketers change their organic (unpaid) social media postings in the near future? A survey by Social Media Exam-iner reported that 65% of B2B marketers (marketers who focus pri-marily on attracting businesses) plan to increase LinkedIn organic social media postings, as compared to 43% of B2C marketers (mar-keters who primarily target consumers). The survey was based on 1,947 B2B marketers and 3,779 B2C marketers. The following table summarizes the results.

		BUSINESS FOCUS
INCREASE LINKED N	B2B	B2C	TOTAL
YES	1266	1625	2891
NO	681	2154	2835
TOTAL	1947	3779	5726

a. Suppose you know that the marketer is a B2B marketer. What is the probability that he or she plans to increase LinkedIn organic social media postings?

b. Suppose you know that the marketer is a B2C marketer. What is the probability that he or she plans to increase LinkedIn organic social media postings?

c. Are the two events, increase LinkedIn postings and business fo-cus, independent? Explain.