## radh 2 years ago Statistics help?

Grades can be converted into numbers (as in calculating a GPA) where an A = 4, B = 3, C = 2, D = 1, and F = 0. For a fictional class, the grade distribution was: X(Grade) 4 3 2 1 0 P(X) 0.20 0.25 0.30 0.10 0.15 a) Verify that this is a legitimate probability distribution. b) Find the mean grade for this class. c) Find the standard deviation

2. lilfayfay

wrong section

openstudy has a stats section?

4. hartnn

could u do part a) ?

5. lilfayfay

yeah

6. lilfayfay

at the top it will say "Find More Subjects"

yeah, I know part a. It's legitimate because the total probability is equal to 1.

8. hartnn

good, thats correct. where r u stuck ?

9. lilfayfay

Yeah its at the very bottom if you click on "Find More Subjects" at the top :))

finding the mean/sd. i found those out, but idk how to corrleate them with the grades. i know mean is .2, so would that mean the average grade is 4 because its' probability is .2?

oh, whoops. i didn't see that before. i'll go there next time.

12. hartnn

mean is 0.2 ? which formula did u use ?

total is 1, divided by 5, .2? did i do that wrong?

14. hartnn

yes... Mean = $$\sum xP(x)$$ so, it will be mean = 0.2*4 + 0.25*3 + ......

oooh. okay. one sec. let me calculate that. :P

2.25?

17. hartnn

don't u have answers to verify ?

18. hartnn

yeah, even i get 2.25

nope. answers are given upon completion. :P

but thanks, I think I got it now. Wrong formula. :P

21. hartnn

and u know formula for sd ?

yeah, got that. i compared that with a friend, and she got the same answer. it was just the mean.

23. hartnn

ok, good :)

24. hanban1

hartnn, if you don't mind could you explain how to find the standar deviation, i'm a bit confused on how to go about it.