Upper Limits and Lower Limits Suppose that a random sample of 12 adults has a me

Question

Upper Limits and Lower Limits

Suppose that a random sample of 12 adults has a mean score of 67 on a standardized personality test, with a standard deviation of 5. (A higher score indicates a more personable participant.) If we assume that scores on this test are normally distributed, find a 90% confidence interval for the mean score of all takers of this test. Then complete the table below. Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place. (If necessary, consult a list of formulas.) What is the lower limit of the confidence interval? What is the upper limit of the confidence interval?

Explanation / Answer

Lower limit = M - Z.95M
Upper limit =   M+   Z.95M

i)

Lower limit = 67-1.645 * 0.90* 67 =67-1.4805=65.51

(For 90% confidence interval Z = 1.645)

ii)

Upper limit=67+1.645 * 0.90* 67 =67+1.4805=68.48

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