00:01
Ok, so we've asked what sampling design did the professor use for his study? so he's done a stratified sample because he's tried to get a proportionate amount of male and female students out of all of his students.
00:18
So he tried to represent both men and women fairly.
00:23
Part b, estimate the mean study hours of all the students and get a 96 percent confidence interval.
00:29
So the mean study hours of all the students, this means pooling the samples of men and women and doing the total study hours divided by the total number of students, which is 50.
00:50
The total study hours is just going to be the mean for the men times the number of men plus the mean for the women times the number of women.
01:00
In.
01:02
And so we get this, and that gives us a mean value of 3 .98.
01:10
The 96 % confidence interval then would be the mean value plus or minus the t value.
01:20
We're using a t value because we don't know the population variance.
01:23
The t value bounding the top and bottom 2 % with 50 minus 1, which is 49 degrees of freedom, times by the standard error, which is going to be given by the pooled standard deviation over the square root of 50.
01:40
Because this is all acting as if it's one sample, so this pooled sample standard deviation is sort of what the standard deviation would be if we took them all together as one sample...