Quote: Construct the confidence interval for the population mean u.
c=0.90, x (it has a line over it)= 15.1, s=7.0, and n=100
A 90% confidence interval for u is (__,__). (Round to one decimal place as needed)
with n=100 your sample variance s' = s/sqrt(n) = s/10 = 7/10 = 0.7
so your sample distribution is Normal(15.1, 0.7)
c=.90 you need the lower tail to be at (1 - .9)/2 = 0.05
looking that up in your table you find that this corresponds to z = -1.64485
Your interval will thus be
(u + z s', u - z s') =
(15.1 - 1.64485*(0.7), 15.1 + 1.64485*(0.7)) =
(13.9, 16.3) to one decimal place.
+4 
+6251 
