Answer: a. CI for the mean: 17.327 < μ < 26.473
b. CI for variance: 29.7532 ≤ ≤ 170.9093
Step-by-step explanation:
a. To construct a 95% confidence interval for the mean:
The given data are:
mean = 21.9
s = 7.7
n = 12
df = 12 - 1 = 11
1 - α = 0.05
= 0.025
t-score = = 2.2001
Note: since the sample population is less than 30, it is used a t-score.
The formula for interval:
mean ±
Substituing values:
21.9 ± 2.200.
21.9 ± 4.573
The interval is: 17.327 < μ < 26.473
b. A 95% confidence interval for the variance:
The given values are:
=
= 59.29
α = 0.05
= 0.025
= 0.975
= 21.92
= 3.816
Note: To find the values for and
, look for them at the chi-square table
The formula to calculate interval:
()
are the lower and upper limits, respectively.
Substituing values:
()
(29.7532, 170.9093)
The interval for variance is: 29.7532 ≤ ≤ 170.9093