help pleasee

#1
I am completely losttttttt & confused...I've tried to solve this with two different formulas.

(smilpling distribution of mean of x1 - mean of x2) its difficult to type the whole formula UGGGGGGGGGGH

Given this information:

Male sample size: 64
Male mean salary (in $1,000): 44
Male Variance: 128

Female sample size:36
Female mean salary (in $1,000): 41
Female Variance: 72




QUESTION:
The 95% confidence interval for the difference between the means of the two population is: ___________________

THE ANSWER:
-0.92 to 6.92



I have absolutely no clue as to how to solve to get the above answer...I'm not even sure I'm using the correct formula...

The point I'm stuck at is (that is if i'm using the right formula) I got the following:
3+/- 98 degrees of freedom .025(2.165063509)
How in the world do you find 98 degrees on the table in my book it goes up to 60 then jumps to 120 then infitinity!?!
 

JohnM

TS Contributor
#2
You don't need to use the t-table and worry so much about degrees of freedom here - the sample sizes are large enough to use the normal distribution tables.

Your textbook most likely has a solved example of computing the confidence interval around the difference between two means....I'd be very surprised if it didn't.:eek:

[(x-bar1) - (x-bar2)] +/- [ 1.96 * SE(x1-x2) ]

where SE(x1-x2) = sqrt[ (v1/n1) + (v2/n2) ]

v=variance
n=sample size