In a class of 30 students,all of whom study history or geography,20 passedo history and 18 passed geography. If xerox is the numBerlin who passedo both history and geography. What is the greatest possible value of x? And the least possible value of x?

To find the greatest and least possible values of x (the number of students who passed both history and geography), we need to consider the number of students who passed each subject.

According to the given information:
- 20 students passed history.
- 18 students passed geography.

We know that the total number of students in the class is 30. However, we don't know how many students studied both history and geography. Therefore, we will consider various scenarios to determine the possible values of x.

Let's consider the greatest possible value of x:
In order to maximize the number of students who passed both history and geography, we should assume that all the students who passed history also passed geography. So, if we assume all 20 students who passed history also passed geography, then the greatest possible value of x would be 20.

Now, let's consider the least possible value of x:
In this case, we assume that none of the students who passed history passed geography, and vice versa. So, we subtract the number of students who passed history (20) and the number of students who passed geography (18) from the total number of students (30):
30 - 20 - 18 = 12
Hence, the least possible value of x would be 12.

To summarize:
- The greatest possible value of x is 20.
- The least possible value of x is 12.