In: Statistics and Probability
A simple random sample with n=56 provided a sample mean of 23.5 and a sample standard deviation of 4.2
Part a)
Confidence Interval
X̅ ± t(α/2, n-1) S/√(n)
t(α/2, n-1) = t(0.1 /2, 56- 1 ) = 1.673
23.5 ± t(0.1/2, 56 -1) * 4.2/√(56)
Lower Limit = 23.5 - t(0.1/2, 56 -1) 4.2/√(56)
Lower Limit = 22.6
Upper Limit = 23.5 + t(0.1/2, 56 -1) 4.2/√(56)
Upper Limit = 24.4
90% Confidence interval is ( 22.6 ,
24.4)
Part b)
Confidence Interval
X̅ ± t(α/2, n-1) S/√(n)
t(α/2, n-1) = t(0.05 /2, 56- 1 ) = 2.004
23.5 ± t(0.05/2, 56 -1) * 4.2/√(56)
Lower Limit = 23.5 - t(0.05/2, 56 -1) 4.2/√(56)
Lower Limit = 22.4
Upper Limit = 23.5 + t(0.05/2, 56 -1) 4.2/√(56)
Upper Limit = 24.6
95% Confidence interval is ( 22.4 , 24.6 )
Part c)
Confidence Interval
X̅ ± t(α/2, n-1) S/√(n)
t(α/2, n-1) = t(0.01 /2, 56- 1 ) = 2.668
23.5 ± t(0.01/2, 56 -1) * 4.2/√(56)
Lower Limit = 23.5 - t(0.01/2, 56 -1) 4.2/√(56)
Lower Limit = 22.0
Upper Limit = 23.5 + t(0.01/2, 56 -1) 4.2/√(56)
Upper Limit = 25.0
99% Confidence interval is ( 22.0 , 25.0
)