The data i'm working with is
Sample mean(voltage)=128.25
variance=9/20
sample size=20
SD=3
Z=-2.61
The first part of what I was doing was a hypothesis test that the true voltage is 130 compared to the alternative less than 130. Which I worked out the Z score to be -2.61
What I have to do now is calculate the critical value for this test using a 1% significance level.. I know the answer is 128.44 but for the life of me I can't work out any formulas that will help me... can anyone shed some light??? Thanks
Is SD = 3 the sample standard deviation or the population standard deviation? If the latter then you probably should be using a t-test, not a z-test.
Regarding the given critical value of 128.44 .... it almost looks like part of a confidence interval .... Were you asked to calculate a confidence interval?
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