& represents 29 students in a class
B represents students who have a brother
S represents students who have a sister
В.
S
7
4
2x
x + 3
7+4+2x+x+3=29
a) One student from the class is chosen at random.
What is the probability that the student has a sister? 14+3x=29
3x=15
X=5
29-8=21