A rhombus thus has all the properties of a parallelogram: Its opposite sides are parallel. Its opposite angles are equal. Its diagonals bisect each other.
The ratio of boys to girls is 4:5. So let 4x be the number of boys and 5x be the number of girls. Then 4x+5x = 9x is the total number of students. Then the fraction of boys in the class is 4x/9x = 4/9.
