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10 May, 04:52

A random sample of 18 graduates of a certain secretarial school typed an average of 80.6 words per minute with a standard deviation of 7.2 words per minute. Assuming a normal distribution for the number of words typed per minute, compute the 95 % prediction interval for the next observed number of words per minute typed by a graduate of the secretarial school.

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  1. 10 May, 06:37
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    Answer: (77.27, 83.93)

    Therefore at 95% confidence/prediction interval is

    = (77.27, 83.93)

    Step-by-step explanation:

    Confidence interval can be defined as a range of values so defined that there is a specified probability that the value of a parameter lies within it.

    The confidence interval of a statistical data can be written as.

    x+/-zr/√n

    Given that;

    Mean x = 80.6 words per minute

    Standard deviation r = 7.2

    Number of samples n = 18

    Confidence interval = 95%

    z (at 95% confidence) = 1.96

    Substituting the values we have;

    80.6+/-1.96 (7.2/√18)

    80.6+/-1.96 (1.697056274847)

    80.6 + / - 3.33

    = (77.27, 83.93)

    Therefore at 95% confidence/prediction interval is

    = (77.27, 83.93)
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