Question 366430
Mall security estimates that the average daily per-store theft is exactly $250, but wants to determine the accuracy of this statistic.  The company researcher takes a sample of 81 clerks and finds
X(BAR) = $210
S = $40.

a) Test at alpha = .001
b) Construct a 90% CIE of u

Feedback:
Part a::::
Ho: u = 250
Ha: u is not equal to 250
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I use a t-statistic for mean problems involving sample size.
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The critical values are +/-3.416337
The test statistic is t(210) =  (210-250)/(40/ sqrt(81)) = -9
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Conclusion: Since the ts is in the rejection interval,
reject Ho.
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Part b:::
 Construct a 90% CIE of u
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x=bar = 210
E = 1.6641*[40/sqrt(81)] = 7.3961
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90% CIE: 210-7.3961 < u < 210+7.3961
90% CIE: 202.6039 < u < 217.3961
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Let me know if this helps.
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Cheers,
Stan H.
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