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    Question about Probability for normal distribution

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    1. Find the probability that a standard normal random variable will assume a value between:
    a. z = 1.5 and z = .75
    b. Greater than 1.25
    c. Find a z such that 70% of the area is above that value.

    2. In recent years, the use of the telephone as a data collection instrument for opinion polls has been steadily increasing. However, one of the major factors affecting the extent to which the telephone can be used is the refusal rate that is, the percentage of eligible subjects actually contacted who refuse to take part in the poll. Suppose that past records indicate a refusal rate of 20% in a large city. What is the probability that out of 15 people:

    a. No one refuses to take part in the poll?
    b. Exactly 2 refuse to take part in the poll?
    c. At most three refuse to take part in the poll?
    d. What is the mean and standard deviation of those who refuse to take part in the poll?

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    Solution Summary

    Calculation of probability based on Z score are discussed here.