91影视

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

The values are categorized as true and false results.

For an event A, the probability of its occurrence is computed as shown below:

$P\left(A\right)=\frac{\text{Number}\text{of}\text{outcomes}\text{resulting}\text{in}A}{\text{Total}\text{number}\text{of}\text{outcomes}}$

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

a.

The total number of subjects is given as follows:

$119+24+154+3=300$

Therefore, the total number of subjects is equal to300.

b.

The number of subjects who had a true negative test result is given by:

$157-3=154$

Therefore, the number of subjects who had a true negative test result is equalto 154.

c.

Theprobability of selecting a subject who had a true negative test result is given as follows:

$$\begin{gathered} P\left(\text{True}\text{negative}\text{result}\right)=\frac{\text{Number}\text{of}\text{subjects}\text{who}\text{had}\text{a}\text{true}\text{negative}\text{result}}{\text{Total}\text{number}\text{of}\text{subjects}} \\ =\frac{154}{300} \\ =0.513 \end{gathered}$$

Therefore, the probability of selecting a subject who had a true negative test result is equalto 0.513.