# Thread: Determine Sample Size

1. ## Determine Sample Size

I'm not sure what direction to go with this problem.

I'm given 2 random samples:
1. 120 men, mean age 26.7, standard deviation 5.2yrs
2. 150 women, mean age 25.1, standard deviation 4.6yrs

I'm required to 1st construct a 98% confidence interval for the difference in the true mean age between men and women.

I've done that... interval (0.19, 3.01)
Bound on the error = 1.41

Now I have to determine the minimum sample sizes necessary to estimate the difference in the population means to with 1 year with a 98% confidence level assuming equla sample sizes of both men and women and using the estimated standard deviations from above.

I can determine the sample size for 1 sample. I'm just not sure how to go about setting up for 2 different samples.

A point in the right direction would be greatly appreciated!!

2. Hi ojvko,

If you've calculated Sp, the pooled standard deviation for the two samples, you can then get the sample size by solving:

2.33*Sp*sqrt(1/n+1/n) = margin of error

2.33 corresponds to 98% confidence.

3. Thanks for the help!!

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