Division by zero is an operation for which you cannot find an answer, so it is disallowed. You can understand why if you think about how division and multiplication are related. But no value would work for x because 0 times any number is 0. So division by zero doesn't work.
- R3KTFORGOOD ☕
Take a look at the picture i sent you
It is not possible to select a single group from the primary school, since being a single group it could not in any way represent the entire primary school.
Choosing a group would provide the average height for that group, not the entire primary.
Assumptions can be made that the course of half of the primary would theoretically give us a more accurate representation, but the objective is to select a number of students from each course and there would be a representative sample of the entire primary.