What are the limitations of the null hypothesis?

Please help with null hypothesis and cutoff score PLEASE?

• A consumer researcher wanted to know if customers really are influenced by sales clerks who smile more. To test this, clerks at seven stores in a large Canadian clothing chain were given special instructions at the start of the week and then sales over the week were recorded. Four of the stores were randomly selected to have the clerks received instructions to be especially courteous and be sure to smile a lot. Clerks at three other stores were simply instructed to be especially courteous. Sales (in the thousands of dollars) for the four stores in the smile condition were 36, 40, 33, and 36; sales for the three stores in the control condition were 40, 31, and 27. Evaluate whether these results suggest that customers are affected if they encounter smiling sales clerks. Use α=.05. What is the null hypothesis? a. The mean sales at a store where the clerks smile a lot is higher than the mean sales at a store where the clerks do not smile a lot b. The mean sales at a store where the clerks smile a lot is not different than the mean sales at a store where the clerks do not smile a lot c. The mean sales at a store where the clerks smile a lot is different than the mean sales at a store where the clerks do not smile a lot d. The mean sales at a store where the clerks smile a lot is lower than the mean sales at a store where the clerks do not smile a lot What cutoff score(s) should be used? a. ±2.571 b. ±2.365 c. +2.571 d. +2.132 Correct decision and conclusion? a. Decision: Reject the null hypothesis; Conclusion: The data support the hypothesis that the mean sales at a store where the clerks smile a lot is higher than the mean sales at a store where the clerks do not smile a lot b. Decision: Reject the null hypothesis; Conclusion: The data support the hypothesis that the mean sales at a store where the clerks smile a lot is lower than the mean sales at a store where the clerks do not smile a lot c. Decision: Do not reject the null hypothesis; Conclusion: The data do not support the hypothesis that the mean sales at a store where the clerks smile a lot is different than the mean sales at a store where the clerks do not smile a lot d. Decision: Do not reject the null hypothesis; Conclusion: The data do not support the hypothesis that the mean sales at a store where the clerks smile a lot is higher than the mean sales at a store where the clerks do not smile a lot

• Answer:

  B, C, B