Answer
95% CI for $μ_d$: $-2.486\lt μ_d\lt-0.180$.
The confidence interval does not contain $µ_d=0$. Reject the null hypothesis.
There is enough evidence to conclude that the two indenters result in different measurements.
Work Step by Step
$H_0:~µ_d=0$ versus $H_1:~µ_d\ne0$
In MINITAB, enter the Steel ball in C1 and the Diamond in C2.
Select Stat -> Basic Statistics -> Paired-t
Select "Each sample is in a column". In "Sample 1" enter C1 and in "Sample 2" enter C2
Click Options. In confidence level enter 95. In Hypothesized difference enter 0. In Alternative hypothesis select difference $\ne$ hypothesized difference. Click OK.
Click OK.
