Suppose you wanted to find out what percentage of upper class Western High students' own cars? You decided to do a stratified sample based on the junior and senior population at school. There are 800 seniors and 1,200 juniors at Western for a total of 2000 students. How many juniors and seniors would you survey if you were to take a sample of 100 students. Hint - This requires a little math - First figure out the percentages of each subgroup to the total number of upper-class students.

Stratified sample refers to a sample that is obtained through a stratified sampling method which divides the total population of interest into smaller groups or strata.

The basis that is used in forming the strata are some common characteristics that the population data have.

From the question, the strata are the seniors and the juniors. The number of juniors and seniors that would be surveyed to take a sample of 100 students can be obtained based on the percentage contribution of each stratum to the total population as follows:

Number of senior population = 800

Number of junior population = 1,200

Total number of studnts = 2,000

Sample to survey = 100

Percentage of senior population in the total population = (Number of senior population / Total number of students) * 100 = (800 / 2,000) * 100 = 0.40 * 100 = 40%

Percentage of juniors population in the total population = (Number of junior population / Total number of students) * 100 = (1,200 / 2,000) * 100 = 0.60 * 100 = 60%

Number of sample of seniors = Percentage of senior population in the total population * Sample to survey = 40% * 100 = 40 seniors

Number of sample of juniors = Percentage of juniors population in the total population * Sample to survey = 60% * 100 = 60 juniors

Therefore, samples 40 seniors and 60 juniors would be surveyed.