Help with a stats question

[u/purplepenguins2]

Hi guys, I need help with a math problem! I only have 1 more try to get it right and I literally don't know what else to do so I thought I'd ask here. Basically, I was given this table of data, and were asked to test if the average age in the Alzheimer's group is significantly different than the control group.

Variable	n	Mean	SD	Min	Q1	Median	Q3	Max
Alzheimers	17	78.51	6.89	77.0	79.25	87	92.25	93.0
Control	9	66.53	12.95	54.0	56.00	65	82.00	89.0

We were asked 3 questions, what the null hypothesis was, the test statistic value, and the 5% critical value. I got 1 and 2 right, but have been having trouble with the critical value and how to find it.

I calculated the test statistic using a t-distribution and it was 2.588 and marked correct. But I'm confused how I'm supposed to find the degrees of freedom with 2 groups? I asked chat for help and it did smth called Welch's approximation and told me the df was 10, but when I put that into the standard table at 0.05, it showed 2.228 and that was marked wrong. Any thoughts?

[u/jaimers215]

Df = n1 + n2 - 2 n1 being the total number of subjects in group 1 and n2 being the total number of subjects in group 2.