Answer:
a)
The degrees of freedom are given by:
The p value for this case would be given by:
Since the p value is significantly lower than he significance level given we have enough evidence to reject the null hypothesis and we can conclude that the true mean is lower than 1425
b) For this case we need to find a critical value in the t distribution with 99 degrees of freedom who accumulates 0.025 of the area in the right tail and we got:
Since the calculated value is higher than the critical value we can reject the null hypothesis at the significance level provided and we can say that the true mean is higher than 1425
Step-by-step explanation:
Information given
represent the sample mean for the cubic feets of households
represent the population standard deviation
sample size
represent the value to verify
represent the significance level
t would represent the statistic
represent the p value
Part a
We want to test that the mean consumption of water per household has decreased due to the campaign by the city council, the system of hypothesis would be:
Null hypothesis:
Alternative hypothesis:
Since we don't know the deviation the statistic is given by:
(1)
The statistic is given by:
The degrees of freedom are given by:
The p value for this case would be given by:
Since the p value is significantly lower than he significance level given we have enough evidence to reject the null hypothesis and we can conclude that the true mean is lower than 1425
Part b
For this case we need to find a critical value in the t distribution with 99 degrees of freedom who accumulates 0.025 of the area in the right tail and we got:
Since the calculated value is higher than the critical value we can reject the null hypothesis at the significance level provided and we can say that the true mean is higher than 1425