Question

If a student who rides the bus to school is selected at random, what is the probability that they are in grade 9?

Answer 1

Step 1: Write out the formula

$Pr(E)=\frac{n(E)}{n(S)}$$\begin{gathered} \text{Where} \\ E\text{ is the event} \\ Pr(E)\text{ is the probability of E happening} \\ n(E)\text{ is the cardinality of E} \\ S\text{ is the sample space or the set of all possible outcomes} \\ n(S)\text{ is the cardinality of S} \end{gathered}$

Step 2: Write out the given values and substitute them into the formula

In this case,

E is the set of grade 9 students who ride the bus to school

From the given table,

$n(E)=3196,n(S)=12681$

Therefore,

$Pr(E)=\frac{3196}{12681}=0.252$

Thus the probability is 0.252