Answer
$T\lt w_{1-α}$: null hypothesis is not rejected.
There is not enough evidence to conclude that $M_x\gt M_y$.
Work Step by Step
Right-tailed test.
Small-sample case:
$T=S-\frac{n_1(n_1+1)}{2}=250-\frac{15(15+1)}{2}=250-120=130$
$w_α=w_{0.05}=73$
(According to table XIII, for $n_1=15$, $n_2=15$ and $α=0.05$)
Critical value:
$w_{1-α}=n_1n_2-w_α$
$w_{0.95}=15\times15-73=152$
Since $T\lt w_{1-α}$, we do not reject the null hypothesis.
