Question

A researcher conducted a study of the access speed of 45 hard drives and concluded that his maximum error of estimate was 25. If he were to conduct a second study to reduce the maximum error to 5, about how many hard drives should he include in his new sample?

Answer 1

Answer to the question)

Given: when number of drives ( N ) = 45

Error ( E) = 25

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Interpretation of variables used in the formula:

• value of Z depends of confidence level
• S = sample standard deviation
• E = Error
• N = Sample size

N = (Z*S / E)^2 [formula of sample size]

45 = (Z * S /25)^2

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on cross-multiplying we get:

(Z *S )^2 = 45 *25^2

(Z*S)^2 = 28125

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If error is 5 , then size would be as follows:

N' = (Z * S)^2 / 5^2

N'= 28125 /25

N' = 1125 [where N' denotes new sample size]