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5.6.8. It is known that some brands of peanut butter contain impurities within an acceptable level. A test conducted on randomly selected 12 jars of a certain brand of peanut butter resulted in the following percentages of impurities: 1.9 2.7 2. 2.8 2.3 3.6 1.4 1.8 2.1 3.2 2.0 Construct a 95% confidence interval for the average percentage of impurities in this brand of peanut butter Give an approximate 95% confidence interval for the population variance. Interpret your results and test for normality

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Answer #1

a)

sample mean =

2.354545

sample sd =

0.653244

Confidence Interval on μ, σ2 Unknown If č and s are the mean and standard deviation of a random sample from a normal population with unknown variance σ. a 100(1 a)% confidence interval for μ is where ta/2 is the t-value with v a/2 to the right n - 1 degrees of freedom, leaving an area of

95 % confidence interval =

(1.916, 2.793)

b)

lower critical value= 3.247

upper critical value = 20.483

he 95% confidence interval is 0.2083 < sigma^2 < 1.3142

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