1. The problem is to find the average (mean) of the given numbers: 85, 79, 82, 78, 65, 43, 66, 69, 80, 91, 40, 79, 81, 70, 55, 60, 71, 50, 77, 75, 74, 74, 80. 2. The formula for the average of $n$ numbers $x_1, x_2, ..., x_n$ is: $$\text{Average} = \frac{x_1 + x_2 + \cdots + x_n}{n}$$ 3. Count the total numbers: There are 23 numbers. 4. Sum all the numbers: $$85 + 79 + 82 + 78 + 65 + 43 + 66 + 69 + 80 + 91 + 40 + 79 + 81 + 70 + 55 + 60 + 71 + 50 + 77 + 75 + 74 + 74 + 80 = 1564$$ 5. Calculate the average: $$\frac{1564}{23} \approx 68.00$$ 6. Therefore, the average of the given numbers is approximately 68.00.