Answer
$t_{\frac{α}{2}}=t_{0.01}=2.567$
Work Step by Step
$n=18$, so:
$d.f.=n-1=17$
$level~of~confidence=(1-α).100$%
$98$% $=(1-α).100$%
$0.98=1-α$
$α=0.02$
$t_{\frac{α}{2}}=t_{0.01}=2.567$
(According to Table VI, for d.f. = 17 and area in right tail = 0.01)
