# Thread: Sum of Squares help!

1. ## Sum of Squares help!

My homework problem says:

For the following summary statistics, find ∑X and SS (sum of squares)

a. XBar = 25, s = 10, n = 11

So, I think that ∑X = 225 but am having trouble how to find SS. Thanks in advance for any help!

2. ## Re: Sum of Squares help!

How are you getting 225?

3. ## Re: Sum of Squares help!

In my notes I have that XBar = ∑X/N .. so I did 25 = ∑X/11 .. 25 x 11 = 225

Is that not right?

4. ## Re: Sum of Squares help!

My homework problem says:

For the following summary statistics, find ∑X and SS (sum of squares)

a. XBar = 25, s = 10, n = 11

So, I think that ∑X = 225 but am having trouble how to find SS. Thanks in advance for any help!
In my notes I have that XBar = ∑X/N .. so I did 25 = ∑X/11 .. 25 x 11 = 225

Is that not right?
your thought process is right but the algebra is where the issue is. try it again in a calculator, how much is 25 x 11?

for the second question here's a small hint. you have the standard deviation. from the standard deviation you can get the variance, right? and if you had real data and not the standard deviation, how is it that you calculate the variance? what would the formula be?

5. ## Re: Sum of Squares help!

Oops, I have 275 written down, not sure why I typed 225.

So, standard deviation = s, which is 10... so to get the variance you just square it, right?

The formula I have is s^2 = ∑(X - XBar)^2 / n-1

6. ## Re: Sum of Squares help!

Well, it will turn out that you have one equation with one unknown when you expand the numerator of the expression (the summation operator expands through the parentheses after the expansion) as you have provided above - given the real constants you have provided.

7. ## Re: Sum of Squares help!

Sorry, I'm not following... How do I find SS?

8. ## Re: Sum of Squares help!

just substitute the values that you already have in the formula for the variance that you wrote in your previous post.

you're so cloooose!!!

9. ## Re: Sum of Squares help!

I am getting so confused because, if I just plug in my values, what am I solving for? In my mind, (which I'm sure is incorrect which is why it isn't making sense...)it's looking like this:

10^2 = (275 - 25)^2 / 10 ... What am I doing wrong? Clearly there's not a variable to solve for. I just don't understand what I am supposed to be doing I guess... the only thing I have written in my notes for SS is Sum of Squares/Degrees of Freedom ... and I can't find much help online as to what SS even is. I feel stumped.

10. ## Re: Sum of Squares help!

all i'm going to say at this point is that the formula for the variance and the formula for the sum of squares are somehow related. and they are related in a non-tricky, you-should-be-able-to-notice-it kind of way.

you can definitely take it from there.

11. ## Re: Sum of Squares help!

I just want to understand...

12. ## Re: Sum of Squares help!

You've already written that you know this:

s^2 = ∑(X - XBar)^2 / (n-1)

Can you identify which part of that is the sum of squares?

13. ## Re: Sum of Squares help!

No, I can't. I don't understand sum of squares. I just started this class, have never had statistics in my life, and I'm trying to understand but I am just getting vague answers and telling me I should just "get it" ... Well, I don't. I have been trying to figure it out for 2 days now.

15. ## Re: Sum of Squares help!

Yes I have a professor, the homework is due Wednesday, which is when I next have class, and I was really having trouble with this problem and stumbled on this website. Made an account hoping to get some help with it. Now I just feel like an idiot since the problem is apparently so simple and I just am missing something. If all of you understand I don't get why you can't help me. Oh well.

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