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tharril
04-22-2010, 08:30 AM
Textbook publishers must estimate the sales of new (first-edition) books. The records of one major publishing company indicate that 10% of all new books sell more than projected, 30% sell close to the number projected, and 60% sell less than projected. Of those that sell more than projected, 70% are revised for a second edition, as are 50% of those that sell close to the number projected, and 20% of those that sell less than projected. a. What percentage of books published by this publishing company go to a second edition? b. What percentage of books published by this publishing company that go to a second edition sold less than projected in their first edition?


How do you go through these questions (the process). The multiple numbers are daunting and causing me to get confused. Any help would be great. Thank you so much!

statsguy
04-25-2010, 01:42 AM
Use a tree diagram.

The probability of a 2nd printing is:

(.10)(.70) + (.30)(.50) + (.60)(.20)

For the second part:
Let A be the probability a book sold less than expected.
Let B be the probability a book was revised.

P(A|B) = P(A \cup B) / P(B)

P(B) is compute in the first part
P(A \cup B) = (.60)(.20)