Exam 7: Sampling Distributions

You stand at the main entrance to a department store and pick the first 20 customers that enter the store after it has opened its door for business on a single day.This is an example of a systematic sample.

The lecturer of a business statistics class wanted to find out the average amount of time per week her students spent studying for the class.Among the 50 students in her class,20% were first-year students,50% were second-year students and 30% were third-year students.She decided to draw 2 students randomly from the first-year students,5 randomly from the second-year students and 3 randomly from the third-year students.This is an example of a stratified sample.

The amount of time required for an oil and filter change on a car is normally distributed with a mean of 45 minutes and a standard deviation of 10 minutes.A random sample of 16 cars is selected.So,95% of all sample means will fall between what two values?