Answer
$t_0\gt-t_α$: null hypothesis is not rejected.
There is not enough evidence to conclude that $µ\lt1.0$
Work Step by Step
$H_0:~µ=1.0$ versus $H_1:~µ\lt1.0$
Requirement:
The population from which the sample is extracted is normally distributed.
$n=19$, so:
$d.f.=n-1=18$
$t_0=\frac{x ̅-µ_0}{\frac{s}{\sqrt n}}=\frac{0.8-1.0}{\frac{0.4}{\sqrt {19}}}=-2.179$
Left-tailed test:
$-t_α=-t_{0.01}=-2.552$
(According to Table VI, for d.f. = 18 and area in right tail = 0.01)
Since $t_0\gt-t_α$, we do not reject the null hypothesis.
