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radh
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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
lilfayfay
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wrong section
radh
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openstudy has a stats section?
hartnn
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could u do part a) ?
lilfayfay
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yeah
lilfayfay
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at the top it will say "Find More Subjects"
radh
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yeah, I know part a. It's legitimate because the total probability is equal to 1.
hartnn
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good, thats correct.
where r u stuck ?
lilfayfay
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Yeah its at the very bottom if you click on "Find More Subjects" at the top :))
radh
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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?
radh
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oh, whoops. i didn't see that before. i'll go there next time.
hartnn
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mean is 0.2 ?
which formula did u use ?
radh
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total is 1, divided by 5, .2? did i do that wrong?
hartnn
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yes...
Mean = \(\sum xP(x)\)
so, it will be
mean = 0.2*4 + 0.25*3 + ......
radh
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oooh. okay. one sec. let me calculate that. :P
radh
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2.25?
hartnn
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don't u have answers to verify ?
hartnn
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yeah, even i get 2.25
radh
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nope. answers are given upon completion. :P
radh
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but thanks, I think I got it now. Wrong formula. :P
hartnn
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and u know formula for sd ?
radh
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yeah, got that. i compared that with a friend, and she got the same answer. it was just the mean.
hartnn
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ok, good :)
hanban1
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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.