In Exercises 9–20, use the data in the following table, which lists drive-thru order accuracy at popular fast food chains (data from a QSR Drive-Thru Study). Assume that orders are randomly selected from those included in the table.

	McDonald’s	Burger King	Wendy’s	Taco Bell
Order Accurate	329	264	249	145
OrderNotAccurate	33	54	31	13

Fast Food Drive-Thru Accuracy If one order is selected, find the probability of getting food that is not from McDonald’s.

The given data shows the number of food orders from four different outlets under two categories, accurate order and inaccurate order.

The probability of an event is computed using the given formula:

$P\left(E\right)=\frac{\text{Number}\text{of}\text{favorable}\text{outcomes}}{\text{Total}\text{number}\text{of}\text{outcomes}}$

Its value ranges from 0 to 1.

The table below shows all the required subtotals and grand total for calculation of probability.

Let A be the event of getting food that is not from McDonald’s.

The total number of food orders that are not from McDonald’s can be denoted as $\overline{m}$.

The value is computed below as:

$$\begin{gathered} \overline{m}=318+280+158 \\ =756 \end{gathered}$$

Let the total number of orders be denoted by N.

The probability of getting food that is not from McDonald’s is given as:

$$\begin{gathered} P\left(A\right)=\frac{\overline{m}}{N} \\ =\frac{756}{1118} \\ =0.676208 \end{gathered}$$

Therefore, the probability of getting food that is not from McDonald’s is 0.676.