Answer:
Step-by-step explanation:
The fact that the student does not have a brother either only means that you have chosen an only child. So there are 13 people that do not have a sister. The 13 comes from the bottom row. 9 + 4 = 13
What is the total number of people in the class? There must be 15 more who do have a sister.
15 + 13 = 28
So the answer should be 13 / 28 or 0.464