Answer
A 90% confidence interval is x +- t x $\frac{s}{\sqrt n}$ = 13.32 +- 1.71 x 22.94 / $\sqrt 25$ = 13.32 +- 7.85.
The percentage of mean time for right-hand threads to that for left-hand ones is 88.7. Therefore, the time saved would be of practical importance.
Work Step by Step
A 90% confidence interval is x +- t x $\frac{s}{\sqrt n}$ = 13.32 +- 1.71 x 22.94 / $\sqrt 25$ = 13.32 +- 7.85.
The percentage of mean time for right-hand threads to that for left-hand ones is 88.7. Therefore, the time saved would be of practical importance.
