Question

A 95% confidence interval for a population mean is determined to be 100 to 120. if the confidence coefficient is reduced to 0.90, the interval for μ

Answer 1

For 95% CI
x - 0.05s = 100
x + 0.05s = 120
Solve for x and s

The interval for u with 90% is 
x - 0.10s
and
x + 0.10s
Substitute x and s