Question

each bus in vivians city has a unique id number. she wants to know how many years a typical city bus has been in service. which method can vivian use to choose a random sample of city buses? list the buses in order from newest to oldest. then, choose the first 20 buses on the list. choose all of the buses that have been in service for more than 20 months. write the id numbers of the 20 oldest buses on cards. then, choose five cards without looking. use a computer to list the id numbers in a scrambled order. then, choose the first 20 buses on the list.

Explanation:

A random sample should be selected without any bias. Listing buses from newest to oldest and choosing the first 20 introduces a bias towards newer buses. Choosing buses with more than 20 months of service is a non - random selection based on a criterion. Writing ID numbers of the 20 oldest buses and then choosing five is also a biased selection towards older buses. Using a computer to scramble the ID numbers and then choosing the first 20 gives each bus an equal chance of being selected in the sample (assuming the scrambling is truly random).

Answer:

Use a computer to list the ID numbers in a scrambled order. Then, choose the first 20 buses on the list.