p value and t test

[Jess16]

I am trying to find the p-value of two sets of data. I have the 2 sample means, standard deviations and sample sizes...I do not have any information about the population.

Data Set 1: xbar= 200 stdev = 30 n= 120
Data Set 2: xbar= 175 stdev = 25 n= 120

I have tried to find p-value using the equations for z and t, but i am getting numbers in the 7-8 range and feel this is too high. I know that you are supposed to use the t-test for things with a sample size 30 or under, but the question also asks for the degrees of freedom, so this makes me assume that i need to use the t-test method. Where am I going wrong, or are the 7ish numbers really right?

Later in the problem i need to find a confidence interval for 99% for the difference btwn the means in the two populations. What is the connection here and do i need one to find the other??

Thanks for the help

 

[tutor_joel]

the equations for t and z are not the correct equations for this since you don't know anything about the population (you don't know mu). Try using the 2 sample t-test. This sheet will also help with the Confidence Interval (CI).