stats
posted by nick .
Nicotine (mg) Filtered Kings
Nonfiltered Kings
n1 = 21
n2 = 8
sample mean = 0.94
sample mean = 1.65
s = 0.31
s = 0.16
Suppose you were to conduct a test (at the 0.05 significance level) to test the claim that kingsize cigarettes with filters have a lower mean amount of nicotine than the mean amount of nicotine in nonfiltered kingsize cigarettes.
For this test, the critical value (to 3 decimal places) is
and the test statisic (to 2 decimal places) is .

You would use a onetailed test for the difference between means. The difference between the means needs to be divided by the standard error (SE) of the difference between means.
SE of the difference between means equals the square root of the sum of the squared SEs of the two means.
The SE for each mean is the standard deviation (s) divided by the square root of n1.
I will leave the calculations to you.
Look up the .05 value in the smaller area in a table of areas under the normal distribution in the back of your text. This will help you find the critical value you seek.
I hope this helps. Thanks for asking.