According to the Yankee Group, 60% of all cable households rate cable companies

Question

According to the Yankee Group, 60% of all cable households rate cable companies as good or excellent in having professional personnel. Suppose 300 cable households are randomly contacted. Use Normal approximation to binomial problems to answer the following question: What is the expected (average) number and standard deviation of cable households that rate cable companies as good or excellent in having professional personnel?

1800; 8.485

180; 120

120; 8.485

1200; 8.485

180; 8.485

1800; 8.485

180; 120

120; 8.485

1200; 8.485

180; 8.485

Explanation / Answer

When we approximate binomial to normal distribution we use the following binomial distribution' formula for mean and standard deviation:

Mean = np = .60*300 = 180
Stdev = sqrt(np*p') = sqrt(.6*300*.4) = 8.485

So, answer is E. 180;8.485

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