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# The life expectancy of computer terminals is normally distributed with a mean of 4 years and a standard deviation of 0.5 year (or 6 months).

1. The life expectancy of computer terminals is normally distributed with a mean of 4 years and a standard deviation of 0.5 year (or 6 months).
a. What percentage of terminals will last less than 4 years?
b. What is the probability that a randomly selected terminal will last more than 5 years?
c. What percentage of terminals will last between 3 and 4.5 years?
d. If the manufacturer guarantees the terminals for 3 years (and will replace them if they malfunction), what percentage of terminals will be replaced?

2. The SAT scores of students are normally distributed with a mean of 950 and a standard deviation of 200.
a. Nancy Bright’s SAT score was 1390. What percentage of students have scores more than Nancy Bright?
b. What percentage of students score between 1100 and 1200?
c. What are the minimum and the maximum values of the middle 87.4% of the scores?
d. There were 165 students who scored above 1432. How many students took the SAT?

5. The following is a frequency distribution of grades of a sample of statistics examinations.

50 - 59 7
60 - 69 10
70 - 79 22
80 - 89 15
90 - 99 6

Compute the following measures:
a. The mean
b. The variance
c. The standard deviation
d. The coefficient of variation

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