T-Stat Question

CFA Level I Quant
#1

Hi,

Just banging out some questions on T-Stats on CFAI and saw this question.

Assuming that the variances of the underlying populations are equal, the pooled estimate of the common variance is 2,678.05. The t -test statistic appropriate to test the hypothesis that the two population means are equal is closest to and the answer is 0.94.

The sample sizes for each population are 25 and 18 and sample means are 200 and 185.

I can’t figure out how they got to that answer, can someone help please? The problem for me is that I don’t understand what has been used as the sample in the standard error calculation

#2

Hi,

The answer is (200-185) / sqrt(2678.05/25 + 2678.05/18) ~= 0.9377 which follows a t with df=25+18-2=41

I have hard time understanding what you mean by standard error calculation. The question assumes unknown but equal variances. Therefore you should use pooled variance as given.

Regards,
Kieren