PostNet wants to estimate the actual mass of documents placed in their medium- sized plastic envelopes (parcel masses) that are couriered to clients throughout the country. A random sample of 43 filled medium-sized plastic envelopes were selected and weighed. Assume that parcel masses (in kg) are normally distributed.
(a) Compute the mean (average) and standard deviation of the sample of parcel weights using theDescriptive Statistics option in Data Analysis. Report these sample findings to the PostNet manager.
(b) Estimate, with a 90% confidence level, the mean parcel mass of all the filled medium-sized plastic envelopes. (Hint: Tick the Confidence Level for Mean box in Descriptive Statistics.)
(c) These envelopes are designed to carry documents that do not exceed 3 kg on average, based on a 90% confidence level. Is PostNet adhering to this requirement? Comment.
(d) Re-compute and confirm the 90% confidence limits using the TINV formula to find the t-limits.