Question

On a school bus there are 10 sixth graders , 4 seventh graders and 6 eighth graders. Calculate the following randomly selected students. A. P( seventh grader) = ?B. P( not seventh grader) =?

Answer 1

In order to calculate the probability of a student from this sample to be a seventh grader, we need to divide the number of seventh graders by the total number of students. This is done below:

`\begin{gathered} P(\text{seventh grader)}=(4)/(10+4+6) \\ P(\text{seventh grader)}=(4)/(20) \\ P(\text{seventh grader)}=(1)/(5) \end{gathered}`

A. The probability of a random selected student being a seventh grader is 1/5.

In order to calculate the probability of the selected student not being a seventh grader, we need to subtract the probability of them being a seven grader from one, because these two events are mutually exclusive. So we have:

`\begin{gathered} P(\text{not seventh grader)}=1-(1)/(5) \\ P(\text{not seventh grader)}=(5)/(5)-(1)/(5) \\ P(\text{not seventh grader)}=(4)/(5) \end{gathered}`

B. The probability of a random selected student not being a seventh grader is 4/5.