Astudent conducts a survey to determine which students at the high school completed an algebra course during their freshman year. 49, 34, and 48 students are selected at random from the sophomore, junior, and senior classes. each class has a population of 496, 348, and 481 respectively. which type of sampling did the student use?

stratified

random

cluster

systematic

Stratified sampling

Stratified sampling is a process of dividing members of the population into homogeneous (separate) subgroups before sampling. Then a random sample is drawn from each group. Members in subgroups may not be fix and subgroups are created under specific type.

Subgroup:  Sophomore, Junior, Senior classes

This sampling technique increases the precision of sampling by reducing sample size especially when population size is too large.

In cluster sampling, a random subset of population is created and then random sample drawn from it. Members of all subgroups are equal.

In systematic sampling, fixed intervals from the larger population create the subset of population. Members of all subgroups are equal.