  ### Home > INT2 > Chapter 4 > Lesson 4.2.4 > Problem4-98

4-98. When Ms. Shreve randomly selects a student in her class, she has a $\frac { 1 } { 3 }$ probability of selecting a boy.

1. If her class has $36$ students, how many boys are in Ms. Shreve’s class?

$P\text{(boy) }=\frac{\text{number of boys}}{36}=\frac{1}{3}$

2. If there are $11$ boys in her class, how many girls are in her class?

$P\text{(boy) }=\frac{11}{x}=\frac{1}{3} \rightarrow x=33$

$\text{# of girls}=33-11$

3. What is the probability that she will select a girl?

The probability of selecting either a boy or a girl should add up to $1$.

4. Assume that Ms. Shreve’s class has a total of $24$ students. She selected one student (who was a boy) to attend a field trip and then was told she needed to select one more student to attend. What is the probability that the second randomly selected student will also be a boy?

Since $\frac{1}{3}\left(24\right)=8$, there are $8$ boys to start out with. However, after $1$ boy is selected, the probability of picking a boy again becomes $\frac{7}{23}$.