degrees of freedom after adding means?


New Member
I have what I suspect is a simple question, but I couldn't apply Wiki's simple explanation and I couldn't understand the more complicated matrix based on.

I am trying to determine if the statistic in group A is larger than that of both B and C combined. I added the means and variances of groups B and C but calculated an unreasonably high t-stastic (t= 13.202) based on 17 degrees of freedom. Among other things I may be doing wrong, I suspect I should loose some degrees of freedom by adding the two groups. If anyone can tell me what the correct number of df should be, and how that is noodled out, I would very much appreciate it. Thank you all for your time and input.

I apologize for not being able to format my table, I am trying to include a little more info than you might need in case I'm wrong about what it is I need. For each group is n=9,5 and 5 for groups AB and C respectively.

Summary Data
Grp mean var n
A 1174.8 122645.7 9
B 490.0 86443.2 5
C 196.7 22800.2 5

Jason Deignan

Also as an extraneous aside, how does one format a tab stop? /t or something?? Sorry, It's post #1 for me. And thanks again!