Question 380538
210, 240, 190, 275, 290, 265, 312, 284, 261, 243.
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sample mean = 257
sample std = 37.16
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a)Find a 90% confidence interval for the average number of new prescriptions written for this new drug among all sales district. What are the assumptions?
E = 1.645*37.16/sqrt(10) = 19.33
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90% CI: 257-19.33 < u < 257+19.33
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b)Calculate the widths of the confidence intervals 

for 95% CI:::Use a z-value of 1.96 in place of 1.645
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for 98% CI::: Usa a z-value of 2.3263
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c)Assuming that the confidence level remains constant, what sample size is needed to reduce by half the margin of error of the confidence interval 
in part (a)?
From part (a): E = 1.645*37.16/sqrt(10) = 19.33
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E/2 = [1.645*37.16/sqrt(10)*(1/2)
E/2 = [1.645*37.16/sqrt(10*4)
Sample size needed = 10*4 = 40
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Cheers,
Stan H.