Question

A proposed null hypothesis states that there is no difference between the mean weights of the population of two neighboring districts. The sample mean difference is 12 kilograms, and the standard deviation of the distribution of the difference between sample means is 9 kilograms. Which statement is true?. A.The null hypothesis must be accepted if we choose the 68% confidence level. . B.The null hypothesis must be accepted if we choose the 95% confidence level.. C.The null hypothesis must be rejected if we choose the 99.7 % confidence level.. D.The null hypothesis must be rejected if we

Answer 1

This is a matter of hypothesis testing.
Null hypothesis: no difference between the mean weights of the population of two neighboring districts

It is important to know the decision rule. At which condition do we reject or accept null hypothesis. 
Example is If p value < significance level, reject null hypothesis.

We then can use the z-statistic. It's best to choose the higher confidence level to account for other results, bias and errors thus, we choose either B or C to be confident in that range of our values.