Asked by Tom

Does studying for an exam pay off? The number of hours studied, x, is compared with the exam grade received, y.

x 7 7 5 5 7
y 95 90 75 85 95

(a) Complete the preliminary calculations: SS(x), SS(y), and SS(xy).
Incorrect: Your answer is incorrect. . (SS(x))
Incorrect: Your answer is incorrect. . (SS(y))
Incorrect: Your answer is incorrect. . (SS(xy))

(b) Find r. (Give your answer correct to three decimal places.)
My answers were (a) 100.9, 19640 and 1396. (B) 7.04 But wrong can someone help????
Answered by MathMate
I do not know if we use the same terminology.
Is SS(x) sum of squares of x?
If it is, I get 197.
Would it be S(xy) instead of SS(xy), meaning just the sum of the products?

Does r mean coefficient of correlation, which has a range of -1 to 1.
If you get 7.04, perhaps you are calculating something else.
Answered by Tom
No it is written in book as (SS(x), so I have not ideal what to do on this one It ask for three answers in first question and 1 answer in the second part and I have missed all of it and I keep coming up with the same answers so I am not sure what I am doing on this one
Answered by MathMate
I was questioning SS(xy) only.
We need Sum of xy for calculating other parameters, but not sum of squares of xy.

How did you get your answers? I got 197 for SS(x). All of your answers seem to come up a little more than half of mine.
Answered by Gayle
197-(31)squared divided by 10 197-961 over 10 = 96.1 then 197-96.1=100.9
Answered by Tom
I did the same thing that Gayle done on this for x and then y which was both wrong answers.
Answered by MathMate
I think you have the right formulas, but the wrong N.

N equals 5 (count either number of x values or number of y values).

So
SSx=197-31²/5=4.8
SSy=39000-440²/5=280
Sxy=2760-31*440/5=32

r=Sxy/sqrt(SSx*SSy)=0.87287
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