Answer:
Cluster sample
Step-by-step explanation:
Samples may be classified as:
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 have that:
Selection of groups according to the buses.
All members on those buses are pulled.
So this is an cluster sample.
Answer:

Step-by-step explanation:
Let x represent Brad's score on 4th test.
We have been given Brad has scored 87, 89, and 78 on the first three.
To find the range of Brad's test score, we will represent our given information in an inequality as:




Therefore, the range of score on the fourth test will be
.