Which technique for gathering data (observational study or experiment) do you think was used in the following studies? explain your answer. (a) the u. s. census bureau tracks population age. in 1900, the percentage of the population that was 19 years old or younger was 44.4%. in 1930, the percentage was 38.8%; in 1970, the percentage was 37.9%; and in 2000, the percentage in the age group was down to 28.5% (the first measured century, t. caplow, l. hicks, b. j. wattenberg).

The provided study is observational study.

Step-by-step explanation:

Consider the provided information.

Observational study: In this study observer only observe the subjects, and measure variables of interest without allocating treatments to subjects.

For example: you want to examine the  side effect of smoke on lung.

Experiment study:The researchers are applying treatments to experimental units in the research, then the effect of the treatments on the experimental units is observed.

The provided study is observational study because measurements of individuals are conducted in a way that doesn't change the response or the variable being measured.

It doesn't matter how many times you perform the study it will result the same.

Thus, the provided study is observational study.

circle area = pi * radius^2

if diameter = 10 then radius = 5

circle area = pi * 5^2

circle area = pi * 25

circle area = 78.5398163397 square units

step-by-step explanation: