Help with this formula please!

G

GGSUS

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Nov 21, 2013
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How do I figure this out given the data?
Σ x^2 - [(Σx)^2/n)]?

x...............................y
2008....................240,300
2009....................246,000
2010....................220,000
2011....................215,000 Is it just [(2008^2)+(2009^2)+(2010^2)+(2011^2)]-[(2008+2009+2010+2011)^2/2]? Thanks for your help! I am studying for my Stats exam in 2 weeks, and I don't have a clue how to solve this :/, I don't have any figures to check to see if I am right or not!
 
GGSUS said:
How do I figure this out given the data?
Σ x^2 - [(Σx)^2/n)]?

x...............................y
2008....................240,300
2009....................246,000
2010....................220,000
2011....................215,000
Is it just [(2008^2)+(2009^2)+(2010^2)+(2011^2)]-[(2008+2009+2010+2011)^2/2]?
Click to expand...
I'm not sure where that final "2" is coming from...? Shouldn't n be equal to 4?

GGSUS said:
I am studying for my Stats exam in 2 weeks, and I don't have a clue how to solve this
Click to expand...
Didn't they cover any of this information in your class? They're kind of supposed to teach the material before giving exams on it! :shock:
 
stapel said:
I'm not sure where that final "2" is coming from...? Shouldn't n be equal to 4?


Didn't they cover any of this information in your class? They're kind of supposed to teach the material before giving exams on it! :shock:
Click to expand...
Ah yes, your right about the 2, thanks! We learned it in early October, and have been learning a lot since then. My professor basically just gave the formula, and final answer (for another question), and I had it wrong the last time. I have probably been getting it wrong because I somehow have been getting the wrong numbers for n. But I understand now :), thanks!
 
GGSUS said:
How do I figure this out given the data?
Σ x^2 - [(Σx)^2/n)]?

x...............................y
2008....................240,300
2009....................246,000
2010....................220,000
2011....................215,000
Is it just [(2008^2)+(2009^2)+(2010^2)+(2011^2)]-[(2008+2009+2010+2011)^2/4]? Thanks for your help! I am studying for my Stats exam in 2 weeks, and I don't have a clue how to solve this :/, I don't have any figures to check to see if I am right or not!
Click to expand...
What you are calculating is n times the Variance. You should remember that the Variance is the same, no matter where you shift x. It will be a whole lot easier if you define year 1 to be 2008:
......n V[x] = Σ x^2 - [(Σx)^2/n)] = (1 + 4 + 9 + 16) - (1 + 2 + 3 + 4)^2 /4 = 5

Likewise when you find Σ y^2 and Σ xy, you can scale y to be thousands.
 
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