Additional Practice for calculating Confidence Intervals for predicted scores

SE estimate = SD for predicted variable * square root of (1 minus the coefficient of determination)
95% CI = estimated Y +/- 1.96 * SE estimate

1) We are using a learner dedication scale (LDS) to predict students' course grades.
The correlation between LDS & course grades is .79.
The SD for course grades is 3.4.
Shan scored a 20 on the LDS, her predicted course grade is 90.
Compute the 95% CI for her score.

2) We are using a learner dedication scale-r (LDS-r) to predict students' course grades.
The correlation between LDS-r & course grades is .89.
The SD for course grades is 3.4.
Shannon scored a 23 on the LDS, her predicted course grade is 92.
Compute the 95% CI for her score.

3) We are using a learner dedication scale-II (LDS-II) to predict students' course grades.
Regression analyses revealed that LDS-II accounts for .88 percent of the variance in course grades.
The SD for course grades is 3.4.
Seyhan scored an 18 on the LDS, her predicted course grade is 85.
Compute the 95% CI for her score.

4) Are you confident that Shan will get a higher grade than Seyhan?
5) Are you confident that Shannon will get a higher grade than Seyhan?