Answer
$\pm 0.445063.$
Work Step by Step
The critical value t using the table with $\alpha=0.02$ and df=27-2=25: $t=\pm 2.485$. Hence, by using the given formula I determine the critival r-values:
$r=\frac{\pm t}{\sqrt{t^2+n-2}}=\frac{\pm 2.485}{2.485^2+27-2}=\pm 0.445063.$
