Question

Can you Please explain me this Question? Thanks!

a) Find z a/2 (two tailed) for the 78% confidence interval.

b) Find t a/2 when n=22 for the 99.5% confidence interval for the mean.

Answer 1

Solution:

a)

At 78% confidence level the z is ,

= 1 - 78% = 1 - 0.78 = 0.22

/ 2 = 0.22 / 2 = 0.11

Z_/2 = Z_0.11 = 1.23

b)

sample size = n = 22

Degrees of freedom = df = n - 1 = 21

At 99.5% confidence level the z is ,

= 1 - 99.5% = 1 - 0.995 = 0.005

/ 2 = 0.005 / 2 = 0.0025

t _/2,df = t_0.0025,21 = 3.135