a) When would the mean grade in class on a final exam be considered a statistic?

b. When would it be considered a parameter?

c. When a student construct a 95% confidence interval, what is his 95% confident about?

a.

A statistic is a measure which is computed for a sample.

The mean grade in class on a final exam be considered a statistic if the class is part of population of students taken for study of mean grades in final exams.

b.

A parameter is a measure which is computed for entire subjects which are aimed for study.

The mean grade in class on a final exam would be considered a parameter if the class forms the entire population. It means the study is being conducted only for students of the class.

c.

When a student constructs a 95% confidence interval, he is 95% confident about the interval that it would contain the true parameter value in the range.

Also, it can be said that he is confident that 95% samples would fall in the interval.