A psychologist was interested in cultural differences compared women of two ethnic groups on a Role Approval Index (high scores mean high degrees of approval of one's social role). The results were as follows:

Ethnic Group A: N = 17 M = 59 S2 = 9.5

Ethnic Group B: N = 28 M = 51 S2 = 2.5

If you conduct a t t est for independent means, how many degrees of freedom are in the t distribution?

1. A)43
2. B)11
3. C)45
4. D)23

Can someone explain why its 28+17-2=43

I need a good explanation or formula explanation. Thank you!