Here is the solution to the provided questions:

(a) The number of people who attended the last 9 screenings of a movie:

Data: $112, 197, 200, 202, 205, 207, 208, 209, 210$

• Mean: Suitable if we want the average value.
• Median: Best for skewed data to represent the middle value.
• Mode: Best when we want the most frequently occurring value.

Since there are no repeated values and the data is nearly uniform, Median is most appropriate as it represents the center of the data.

Answer: Median

(b) On a test, each student is given a grade (A, B, C, D, or F):

• Mean: Not applicable for categorical data.
• Median: Suitable for ordinal data, but not for frequency-based evaluation.
• Mode: Best for identifying the most frequently occurring grade.

Since the question asks about the most frequent grade, Mode is the correct choice.

Answer: Mode

(c) The last 10 calls to a customer support line had these durations (in minutes):

Data: $22, 23, 24, 25, 26, 27, 28, 29, 30, 31$

• Mean: Represents the average.
• Median: Represents the middle value.
• Mode: Represents the most frequent value.

The data is evenly distributed with no repeated values. Therefore, the Mean provides the best summary of the overall duration.

Answer: Mean

Do you have further questions or need detailed calculations for these? Here are five related follow-ups you might consider:

1. What is the formula for calculating the mean and how does it differ from median calculation?
2. How can you identify skewed data and choose between mean or median in such cases?
3. When should mode be used for numerical data instead of mean or median?
4. Can ordinal data (like grades) be averaged, and why or why not?
5. How can outliers affect the choice of mean vs. median?

Tip: Always consider the type of data (categorical vs. numerical) when choosing an appropriate statistical measure.