Answer
$k\gt critical~value$: null hypothesis is not rejected.
There is not enough evidence to conclude that $M\lt15$.
Work Step by Step
$H_0:~M=15$ versus $H_1:~M\lt15$
$number~of~plus~signs=7$
$number~of~minus~signs=8$
$n=7+8=15$ (small sample)
$Critical~value=3$
(According to table XI, for $n=15$ and $α=0.05$ (one tail))
Right-tailed test:
$k=number~of~plus~signs=7$
Since $k\gt critical~value$, we do not reject the null hypothesis.
