To figure out the probability of a student who has a brother not having a sister, we need to consider the number of students who have a brother and do not have a sister.
Given the information provided:
- There are 18 students in total.
- 5 students have a brother.
- 7 students have a sister.
- 9 students have neither.
To find the number of students who have a brother without a sister, we need to subtract the number of students who have both a brother and a sister from the total number of students with a brother.
Number of students who have a brother and a sister = 0 (since it is not stated in the given information)
Number of students who have a brother without a sister = 5 - 0 = 5
Therefore, there are 5 students who have a brother without a sister.
To calculate the probability, we divide the number of favorable outcomes (students who have a brother without a sister) by the total number of possible outcomes (total number of students with a brother).
Probability of a student who has a brother not having a sister = Number of students who have a brother without a sister / Number of students who have a brother
Probability = 5 / 5 = 1
The probability of a student who has a brother not having a sister is 1 or 100%.