Answer:
Difference between upper and lower limits is : 1,816
Step-by-step explanation:
A CI (confidence interval ) for t student distribution is:
( μ₀ - t(α/2)* s/√n ; μ₀ + t(α/2)* s/√n )
Where:
μ₀ is the mean and s the standard deviation of the dstribution
n size of the sample
CI = 90 % means α = 10 % α = 0,1 α/2 = 0,05
and degree of freedom df = n - 1 df = 40
From t student table we get:
tα/2 = 1,6839
Then:
t(α/2)* s/√n = 1,6839* 3,41/√40
t(α/2)* s/√n = 0,908
8,73 - 0,908 = 7,822
8,73 + 0,908 = 9,638
CI (90%) = ( 7,822 ; 9,638 )
Difference between upper and lower cut-offs points is:
Δ = 1,816
