Find the 90% two-sided confidence interval for the mean score.

[ianrice]

The distribution of grades is know to follow a normal distribution, but the mean and variance are unknown. A random sample of 12 students produced the following scores:

59, 84, 68, 93, 49, 77, 82, 75, 81, 58, 70, 80

Find the 90% two-sided confidence interval for the mean score.

 

[Stephen Tashi]

The distribution of grades is know to follow a normal distribution

Does this grading system allow negative grades? If not, the the grades can't actually be normally distributed.

Of course, perhaps this is a homework problem where such technicalities are ignored. If so, you should post it somewhere in the "Homework & Coursework Questions" section of the forum and show your attempt at solution.

 

[statdad]

"Does this grading system allow negative grades? If not, the the grades can't actually be normally distributed."

Nothing is ever really normally distributed: if the standard deviation is small enough then to a very good approximation the normal distribution can be quite useful.

 

[DrDu]

You might consider a Student's t-distribution