PLEASE HELP
The California Board of Education wants to know how 5th grade students are doing in math this year. They get a list of all 5th graders in the state of California and look at the overall math grades of every 10th student on the list. Then they add the scores and divide to get an average. What kind of sampling is this?

random sampling
responses to a survey
add and divide survey
biased sampling

Question

PLEASE HELP 
The California Board of Education wants to know how 5th grade students are doing in math this year. They get a list of all 5th graders in the state of California and look at the overall math grades of every 10th student on the list. Then they add the scores and divide to get an average. What kind of sampling is this?

    random sampling
    responses to a survey
    add and divide survey
    biased sampling