# Help With Homework Problem Please

#### KnifeRun

##### New Member
Hi, I've got this question that I'm unsure about how to approach. I was wondering if anyone could give me a hand or steer me in the right direction.

I've got some sample data.. what it represents isn't really important. The first group is 782, 965, 948, 1181, 1414, 1633, 1852. The second group is 593, 672, 750, 988, 1226, 1462, 1698. The means of each I calculated to be about 1253 and 1055 respectively.

The question is to find a 95% confidence interval for the different in the means. I'm confused because no standard deviation is given (and usually is in our class), so I'm a bit unclear as how to standardize this to find the CI using the methods I know about. Can anyone help me out?

#### JohnM

##### TS Contributor
You compute the standard deviation for each sample and use them as estimates of the true standard deviation in the population.

In order to find a conf int for the difference between the means, you will need to pool the standard deviations (sort of like a weighted-average std dev).

#### KnifeRun

##### New Member
JohnM said:
You compute the standard deviation for each sample and use them as estimates of the true standard deviation in the population.

In order to find a conf int for the difference between the means, you will need to pool the standard deviations (sort of like a weighted-average std dev).
Thanks a lot.. I think I got it figured out!