Question

A survey was mailed to a total of 400 students; 100 were randomly selected from each of the freshman, sophomore, junior and senior classes last semester. What sampling method was used?

Answer 1

There are many different types of sampling methods. Check them out and see which one closely fits your scenario.

Answer 2

Let smokers =A.
Gum chewers=B
n(AuB)= n(A) + n(B) -n(AnB).
100 + 150 - 75
=250-75=175
neither =400-175=225