If a number has 20 as a factor, what other factors must it also have? (Write your answers in ascending order.)
1-0-000

Elijah should interview every 5th student who enters the building in the morning. It would be a stratified sampling where Elijah will take a sample from each one out of five students.

The other methods would be a biased sampling as students who are in a school band or attending a concert or wearing earbuds in the cafeteria would likely to give a 'yes' answer.