In Eva's grade, 2/3 of the students have a sister. Of the students who have a sister, 1/2 also have a brother. What fraction of the students in Eva's grade have both a sister and a brother?
Let's assume there are a total of x students in Eva's grade.
2/3 of the students have a sister, which means (2/3)x students have a sister.
Among these students, 1/2 also have a brother, which means (1/2)(2/3)x = (1/3)x students have both a sister and a brother.
Therefore, the fraction of students in Eva's grade who have both a sister and a brother is 1/3.