Question

# A class has 20 girls and 16 boys. One student is selected at random. Find the probability that the selected student is a girl.A. $\dfrac{1}{4}$B. $\dfrac{5}{9}$C. $\dfrac{3}{4}$D. $\dfrac{4}{9}$

Hint: In this particular problem find the total number of students and then use the probability formula for finding probability of getting a girl on selection. Formula for probability of getting a favourable outcome is = $\dfrac{{{\text{Number of favourable outcomes}}}}{{{\text{Total number of outcomes}}}}$
As we know from the concept of the probability that if there are n balls out of then x are of same type A then the probability of getting a ball of type A on random selection is equal to = $\dfrac{{{\text{Number of favourable outcomes}}}}{{{\text{Total number of outcomes}}}}$. So, in this example favourable outcome will be ball of type A. So, probability = $\dfrac{{{\text{Number of balls of type A}}}}{{{\text{Total number of balls}}}} = \dfrac{x}{n}$
So, probability that the selected student is girl = $\dfrac{{{\text{Number of girls}}}}{{{\text{Total number of students in class}}}} = \dfrac{{20}}{{36}} = \dfrac{5}{9}$