A previous study of nickels showed that the standard deviation of the weight of nickles is 100 milligrams. A coin counter manufacturer wishes to find the 99% confidence interval for the average weight...

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We want to test left tailed hypothesis:
H0 : σ
2 ≥ 9 (Null Hypothesis, H0 : σ2 = 9 is also correct)
Ha : σ
2 < 9 (Alternative Hypothesis, also called H1)
Given: s = 2.494 ⇒ s2 = 6.220 036, n = 25
Signi�cance level, α = 0.05
Degrees of freedom, df = n − 1 = 24
Since this is left tailed test, we need area of α = 0.05 on the left of critical value.
This means area of 0.95 on right of critical value. Critical value is given by
χ21−α = χ
2
0.95
with 24 degrees of freedom. We can use chi-square table or excel
command
CHISQ.INV(0.05, 24) =...