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:

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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