Question

ellen wonders what pets the students at her school prefer. so, she plans to ask a small sample of them. pick all the ways of sampling the students that would produce a representative sample. ellen assigns a number to each student. she uses a computer to randomly pick 20 of them to ask. ellen randomly chooses a dog park. she asks 20 students she sees there. at ellens school, teachers assign seats randomly. ellen asks 2 students who sit in the front row of each of the 10 science classes.

Explanation:

A representative sample should be unbiased and reflect the entire student - body. Assigning a number to each student and randomly picking some is a form of simple random sampling which is unbiased. Asking students at a dog - park is biased as those students are more likely to like dogs. Asking students in the front row of science classes may be biased as it only samples from science classes and a particular seating position. But among the given options, the first and third methods have some randomness and can be considered to have a better chance of being representative compared to the dog - park method.

Answer:

Ellen assigns a number to each student. She uses a computer to randomly pick 20 of them to ask.
At Ellen's school, teachers assign seats randomly. Ellen asks 2 students who sit in the front row of each of the 10 science classes.