<span>I believe the degrees of freedom in this case is 19. As I understand N is the number of participants as there are 20 students. Subtract one for statistical purposes puts that number at 19. The other option might have to deal with the total number of variables however I believe N is the basis here.</span>
The answer to your question, would be that the result of landlords not maintaining their tenements got injured because they were in unsafe living spaces.
<span>A strong central government</span>