Arandom sample of 121 automobiles traveling on an interstate showed an average speed of 65 mph. from past information, it is known that the standard deviation of the population is 22 mph. if we are interested in determining an interval estimate for μ at 96.6% confidence, the z value to use is

The z-value would be 2.12.

We first find our α value.  We convert our confidence level to a decimal number, subtract from 1, and divide by 2:

96.6%=96.6/100 = 0.966
α = (1-0.966)/2 = 0.034/2 = 0.017

We now subtract this from 1:
1 - 0.017

This is the value we look up in a z-table (http://www.z-table.com).  This corresponds with a z-value of 2.12.

It’s d for sure i just did also that’s why