91影视

The given data shows the number of positive and negative drug test results of the subjects.

The values are categorized as true and false results.

For two events A and B, the probability of occurrence of only A, only B, or both is computed as shown below:

$P\left(A\text{or}B\right)=P\left(A\right)+P\left(B\right)-P\left(A\text{and}B\right)$

Here, $P\left(A\text{and}B\right)$ is the probability of A andB occurring together.

The table below shows the number of subjects that fall into each category:

The total number of subjects is equal to 300.

Let E be the event of selecting a subject who tested negative.

Let Fbe the event of selecting a subject who used marijuana.

The number of subjects who tested negative is equal to 157.

The number of subjects who used marijuana is equal to:

$$\begin{gathered} \text{True}\text{Positive}+\text{False}\text{Negative}=119+3 \\ =122 \end{gathered}$$

So, the corresponding probabilities are:

$$\begin{gathered} P\left(E\right)=\frac{157}{300} \\ P\left(F\right)=\frac{122}{300} \end{gathered}$$

The number of subjects who tested negative and used marijuana is equal to the number of subjects who tested false. Thus, it is equal to 3.

$P\left(E\text{and}F\right)=\frac{3}{300}$

Theprobability of selecting a subject who tested negative or used marijuana is equal to:

$$\begin{gathered} P\left(E\text{or}F\right)=P\left(E\right)+P\left(F\right)-P\left(E\text{and}F\right) \\ =\frac{157}{300}+\frac{122}{300}-\frac{3}{200} \\ =\frac{276}{300} \\ =0.92 \end{gathered}$$

Therefore, the probability of selecting a subject who tested negative or used marijuana is equal to 0.92.