Yeah It's a weird question. The data I'm given is sample standard deviation and it is a normal distribution. The entire quesiton says The Output voltage of a circuit is specified to be 130. A sample of 20 independent readings gave the mean reading as 128.25. Assume normal distribution with

=3

So the quesiton says test the hypothesis that the true output voltage is 130 against the alternative it is less than 130, and I used a fomula that I thought was Z=128.25-130/(3/(sqrt(20)) and ended up with -2.61 (which is the correct answer)

So the part I'm stuck on is, What is t he critical value for the test in the part above using a 1% significance level.

I thought it might be a confidence interval but I couldn't figure it out? The answer just says "Critical Value = =128.44