statistics excel

Question

excel spreadsheet showing all calculations.

A breakfast cereal manufacturer is concerned that their boxes of cereal are not being filled properly. According to the labels, each box should contain 375 grams of cereal. The analysis of a sample of 30 boxes indicates the average weight is 370 grams with a standard deviation of 7.09 grams.
Test whether the average number of grams is different from what is officially claimed, to a 90% confidence level. What can you determine?

Answer 1

Ancient junk, Please get rid of these old remnants.

As for the question, the CI on the estimate based on a set of 30 samples is xbar [370g] ± 1.645

1. 7.09/√30 or (367.87 372.13). Since the confidence interval does NOT contain the desired weight of 375 g, then we have to reject the null hypothesis (i.e. no difference) and assume that the weight of the packages are low. Shame on you Mr Manufacturer.