Retailing and Large Online Retailers

Problem set 3
Crystal Yu

1. Do problem 4.8 and 4.9 page 149 (2 points) You need to show your work to get credit.

4.8
Does it take more time to be removed from an email list than it used to take? A study of 100 large online retailers revealed the following:

Need Three Or More Clicks to Be Removed

Year Yes No Total
2009 39 61 100
2008 7 93 100 46 154 200

a. Give an example of a simple event
Need less than 3 more clicks to be removed.
b. Give an example of a joint event
Need three or more clicks to be removed in 2008
(2 events : needs 3 or more clicks and happened in 2008)
c. What is the complement of "Needs three or more clicks to be removed from an email list"? Need less than 3 more clicks.
d.Why is "Needs three or more clicks to be removed from an email list in 2009" a joint event?
It neeeds to fit both criteria, 3 or more clicks and occur in the year 2009

4.9

Referring to the contingency table in Problem 4.8, if a large online retailer is selected at random, what is the probability that

a. you needed three or more clicks to be removed from an email list?
P = 46/200 = 23%
b. you needed three or more clicks o be removed from an email list in 2009?
P = 39/200 = 19.5%
c. you needed three or more clicks to be removed from an email list or were a large online retailer surveyed in 2009?

Let say event A = "needed three or more clicks to be removed from an email list" --> P(A) = 23% Let say event B = "were a large online retailer surveyed in 2009" ---> P(B) = 100/200 = 50% So P(A or B) = P(A) + P(B) - P(A and B) = 23% + 50% - 19.5% = 53.5%

d. Explain the difference in the results in (b) and (c).

2. Do problem 4.21 page 157 (2 points) You need to show your work to get credit.
Table
Year Yes No Total
2009 39 61 100
2008 7 93 100