Jamal suspects that his diastolic blood pressure is higher when he is at work than his diastolic blood pressure when he is not at work.

2. Jamal suspects that his diastolic blood pressure is higher when he is at work than his diastolic blood pressure when he is not at work. He is going to test this statement based on blood pressure readings at randomly selected times in the above two situations. 

Here are the data (units in mmHg) 

at work 84 84  86  86  87  87  87  88  90  97  99  not at work   77  78  79  79  80  83  84  85  85  89  

a) Why should we not use the two sample t-test in this case?  

b) Use the Wilcoxon Rank Sum test with normal approximation to test if the BP readings at work are higher than the readings when not at work. Write the P_value and your conclusion at 5% level of significance