Math
posted by Willow .
There are 12 girls and 9 boys in Mrs. Johnson's classroom. She said that if she randomly selects one student from her classroom the probability that it is a boy is 3/4. Which mistake did Mrs. Johnson make?
A. She divided the number of girls by the total number of students.
B. She divided the number of boys by the total number of students.
C. She divided the number of girls by the number of boys.
D. She divided the number of boys by the number of girls.

Which process will give you 3/4? Do the math to find out.