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PROBABILITY
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2. 7.5 Conditional Probability and Independent Events
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3. More on Tree Diagrams

4. Applied Example 6 – Quality Control
The panels for the Pulsar 32-inch widescreen LCD HDTVs are manufactured in three locations and then shipped to the main plant of Vista Vision for final assembly. Plants A, B, and C supply 50%, 30%, and 20%, respectively, of the panels used by the company. The quality-control department of the company has determined that 1% of the panels produced by Plant A are defective, whereas 2% of the panels produced by Plants B and C are defective.
What is the probability that a randomly selected Pulsar 32-inch HDTV will have a defective panel?

5. Applied Example 6 – Solution
Let A, B, and C denote the events that the HDTV chosen has a panel manufactured in Plant A, Plant B, and Plant C, respectively. Also, let D denote the event that a HDTV has a defective panel.
Using the given information, we draw the tree diagram shown in Figure 19. (The events that result in a HDTV with a defective panel being selected are circled.)
Tree diagram showing the probabilities of producing defective panels at each plant
Figure 19

6. Applied Example 6 – Solution
cont’d
Taking the product of the probabilities along each branch leading to such an event and then adding them, we obtain the probability that a HDTV chosen at random has a defective panel.
Thus, the required probability is given by
(.5)(.01) + (.3)(.02) + (.2)(.02) =
= .015

7. Practice
p. 408 Self-Check Exercises #2