A random sample of 138 observations produced a sample mean of 30. Find the critical and observed values of z for the following test of hypothesis using α=0.1. The population standard deviation is known to be 9 and the population distribution is normal.
H0: μ=28 versus H1: μ≠28.
Round your answers to two decimal places.
zcritical left =
zcritical right =
zobserved =