Answer
$ \begin{array}{ll}
a. & 1.833\\
b. & \pm 1.740\\
c. & -3.365\\
d. & 2.306
\end{array}$
Work Step by Step
For each part, use the table for the $t$-distribution.
Recall that t-values in the left tail are negative, and in the right tail, positive.
Also, recall that the test statistic follows a $t$-distribution with $n-1$ degrees of f reedom.
$a.$
In the row
$d.f.= 10-1=9$,
find the intersection with the column "one tail, $\alpha=0.05$"
Critical value: $1.833$
$b.$
In the row
$d.f.=18-1=17$,
find the intersection with the column "two tails, $\alpha=0.10$"
Critical values: $\pm 1.740$
$c.$
In the row
$d.f.= 6-1=5$,
find the intersection with the column "one tail, $\alpha=0.01$"
Critical value: $-3.365$
$d.$
In the row
$d.f.= 9-1=8$,
find the intersection with the column "one tail, $\alpha=0.025$"
Critical value: $2.306.$
