Answer:
0.185
Step-by-step explanation:
Given:
                    Has a brother       Does not have a brother
Has a sister               5                     7
Does not have a sister      11                     4
So, The total number of the students in the class = 5 + 7 + 11 + 4 = 27
The number of student has a sister given that they have a brother = 5
∴ The probability = 5/27 = 0.185
The probability that a student has a sister given that they have a brother = 0.185