Answer:
The sampling technique used is the stratified technique.
Explanation:
We have these following sampling techniques:
Random: Basically, put all the options into a hat and drawn some of them.
Systematic: Every kth element is taken. For example, you want to survey something on the street, you interview every 5th person, for example.
Cluster: Divides population into groups, called clusters, and each element in the cluster is surveyed.
Stratified: Also divides the population into groups. However, then only some elements of the group are surveyed.
In this problem:
We select some math majors, some music majors and some history majors.
That is, the population is divided into groups, and some elements of each group is surveyed.
So the sampling technique used is the stratified technique.