Random sample of math scores assumed to be : X1=644, X2=493, X3=532, X4=462, X5=565

Random sample of verbal scores assumed to be : Y1=623, Y2=472, Y3=492, Y4=661, Y5=540, Y6=502, Y7=549, Y8=518

How do I find a 90% confidence level for ?

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- Jun 11th 2009, 07:32 AMmadgabFind 90% confidence interval
Random sample of math scores assumed to be : X1=644, X2=493, X3=532, X4=462, X5=565

Random sample of verbal scores assumed to be : Y1=623, Y2=472, Y3=492, Y4=661, Y5=540, Y6=502, Y7=549, Y8=518

How do I find a 90% confidence level for ? - Jun 11th 2009, 10:01 AMdrichie
hint:

If and are independent normal random variables, then:

- Jun 11th 2009, 03:12 PMmatheagle
This one is finally well worded.

You want to pool the sample variances because we are assuming that the two population variances are equal.

It will be a t with degrees of freedom.

see.. Unequal sample sizes, equal variance (Ignore uequal sample size comment)

at http://en.wikipedia.org/wiki/Student's_t-test - Jun 12th 2009, 08:25 AMmadgab
Thank you! That site was extremely helpful. I am now working on plugging all the correct values in to get a "normal" sounding answer. Thank you for helping me.

- Jun 12th 2009, 05:27 PMmatheagle
- Jun 14th 2009, 09:27 AMmadgab

(seems high)

This answer doesn't seem quite right.

Then how do I do the confidence interval using the 90% CI, 1.645?

I was going to just do

but neither of my answers seemed to make any sense. - Jun 16th 2009, 07:44 AMmadgab
Thank you for all the help on this problem. I do not understand why the population variances are equal, or how you figure that. I have been going through different books and thought I could just use the equation that uses just the sample means and variances with the t value from the table. I'm sure I'm wrong, I just can't figure out how to tell that the pop variances are equal. Thanks

- Jun 16th 2009, 07:56 AMmatheagle
- Jun 16th 2009, 08:04 AMmadgab
I got it! Thank you! I'm sorry for bothering you again. It all makes sense now.