Answer:
2/9
Explanation:
If the question were what is the probability a student has no sisters bu has a brother, then the answer would be 2/23.
Here, we are dealing with conditional probability.
Read carefully the question "What is the probability that a student who does not have a sister has a brother?"
Here, you are not looking at all students. You are only looking at students who have no sister.
Look at the bottom line of the table.
That line deals only with students who have no sisters.
The total of the line is 9 students.
None of those students have sisters.
Out of the 9, 2 students have a brother, and 7 of the students do not have a brother.
Answer: 2/9