Question: Mrs. Ricco has seven brown-eyed and one blue-eyed brunettes in her fifth grade class. She also has nine blue-eyed and three brown-eyed blondes. A child is selected at random,what is the probability that the child is a brown-eyed brunette?  Edit

Answer: Total no of blue eyed=1+9=10
and total brown eyed =7+3=10
Total no of child=10+10=20
You can select a child out of 20 by 20C1 ways.
So, n(S)=20C1=20
Let E=event of selected child is a brown-eyed brunette
n(E)=7C1=7
Therefore, P(E)=n(E)/n(S)=7/20 =0.35=35% (Ans.)  Edit