Doing a t-test I got this results :

**200 400**

Mean 944.58333 960

Variance 402.08333 222.727273

Observations 12 12

Pooled Variance 312.4053

Hypothesized Mean Difference 0

df 22

t Stat -2.13652

P(T<=t) one-tail 0.0220045

t Critical one-tail 1.7171444

P(T<=t) two-tail 0.0440091

t Critical two-tail 2.0738731

According with my notes if t Stat < -t Critical two-tail or t Stat > t Critical two-tail, we reject the null hypothesis. This is the case, means are unequal. But statgraphics tells me that means are equal. Someone could help me with this?

Thank you for your support.