Formulating null/alternate hypotheses, parameter of interest, general statistics help!

Having some extreme difficulty with a college assignment and any help/guidance whatsoever would be greatly appreciated!

ESB (Irish electricity board) believe that the demand for electricity has fallen on average since the onset of the economic crises. Prior to the downturn, mean electricity demand was 4000MW, with a standard deviation of 948MW. Using the mean (3,572.340) and standard deviation of your sample, conduct a hypothesis test using a 95% confidence level.

(1) Specify the population parameter of interest.
(2) Formulate the null and alternate hypothesis.
(3) Specify the significance level.
(4) Construct the rejection region.
(5) Compute test statistic.
(6) Reach a decision.
(7) Draw a conclusion.

Rosie -


(1) Specify the population parameter of interest.

The parameter is the population "mean" electricity demand


(2) Formulate the null and alternate hypothesis.

Ho: mean = 4000
Ha: mean < 4000


(3) Specify the significance level.

alpha = 5%

(4) Construct the rejection region.

P(Z < z) = 0.05. Looking this up in a Standard Normal table:

z = -1.645

So, rejection region is either p < 0.05 or z < -1.645


(5) Compute test statistic.

z-statistic = (3,572.340 - 4000) / 948 = -0.45


(6) Reach a decision.

p-value = P(z < -0.45) = 0.33

Since p > 0.05, DO NOT REJECT

(7) Draw a conclusion.

There is significant evidence at the 5% significance level that the mean is not less than 4000

Hope that helps