In a class, there are 12 boys and 16 girls. One of them is called out by an enroll number, what is the probability that the one called is a girl?

Answer: Option C

Let S be the sample space
Total number of students in the class = 12 boys + 16 girls = 28
Then, n(S) = 28
Let E be the event of calling one of them by enroll number
Given that, number of girls = 16
Then, n(E) = 16
The probability that the one called is a girl
$$\begin{array}{rl}& =\frac{\text{n}\left(\text{S}\right)}{\text{n}\left(\text{E}\right)}\\ & =\frac{16}{28}\\ & =\frac{4}{7}\end{array}$$