State the sampling technique used stratified, random, cluster, convenience or systemic if a researcher divides the ages of people in the community into four groups first group less than 20 years old, second is greater or equal to 20 but less than 40 years old, third is greater or equal to 40 but less than 60 years old and fourth is greater than or equal to 60 years old. the researcher then takes a random sample from each group