# Essay on Retailing and Large Online Retailers

751 Words Nov 13th, 2013 4 Pages
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
…show more content…
There were 46 retailers surveyed in two years that need three or more clicks to be removed, 39 of them happened in 2009 --> So P = 39/46 = 84.78%

b. Given that the year 2009 is involved, what is the probability that three or more clicks are needed to be removed from an email list?
Of 100 retailers surveyed in 2009, 39 need there or more clicks to be removed ---> So P = 39/100 = 39%

c. Explain the difference in the results in (a) and (b).
Results in (a) and (b) are different because the conditions are different. Condition of (a) means for those retailers that “needed three or more clicks to be removed” how many were surveyed in 2009. While condition of (b) means the opposite way, for those surveyed in 2009, how many retailers need 3 or more clicks.

d. Are needing three or more clicks to be removed from an email list and the year independent?
They are not independent. Refer to Equation 4.5 in textbook, p.154 shows that two events A and B are independent if and only if P(A│B) = P(A)
Calculate the probabilities of the events :
P(need three or more clicks to be removed) = 46/200 = 23%
P(need three or more clicks to be removed given condition that occurred in 2009) = 39%

Chapter 6 Individual work

Using a Normal Distribution to find probabilities: You may use the tables in your text or PhStat – Probability Distributions – Normal. Regardless of which method you use, either draw a sketch and