Question 456932
n=20, m=58, s=12
(a, b)=m +- z[a/2] * s/sqrt(n)
(a, b)=58+-1.645*(12/sqrt(20)) The z for .9 confidence level 2 tailed is +-1.645
=58+-4.41
=(62.41, 53.59)
.
Ed