Question

Before any order is shipped, inspectors at AlvarezManufacturing test a sample of finished units for breakingstrength. You select a simple random sample of units from arecently completed order and find that the sample averagebreaking strength is 814 pounds. From the sample selected,you construct a 95% confidence interval estimate of the average breaking strength you could expect to find if all the units in the order were tested. The interval turns out to be 814 7.5 lbs. How would you interpret your result?

A) Approximately 95% of the units in the order will have abreaking strength of between 806.5 lbs. and 821.5 lbs.

B) Approximately 95% of the units in the sample have a breaking strength of between 806.5 lbs. and 821.5 lbs.

C) Approximately 95% of the units in the population will have abreaking strength of between 806.5 and 821.5 lbs.

D) We can be 95% confident that all the units in the order have a breaking strength of between 806.5 lbs. and 821.5 lbs.

Answer 1

The correct answer is the third option, i.e. option C. Approximately 95% of the units in the population will have a breaking strength of between 806.5 and 821.5 lbs.

The interval shows the distribution of the population. Hence, it should have a meaning attached to the entire lot i.e. the population.