Question

I don't know how to do it but I at least think it could either be C or D... Please help me.

Answer 1

We could draw a table to help us to answer this question.

                  Took medication         Didn't take medication         Total
No cough               17                                   28                          45
Cough                    13                                   42                          55        
Total                       30                                   70                         100        

The question states "given that they reported no cough", which is basically asking how many people OUT OF those who reported no cough took the medication.

So using the table, the number of people who took the medication and reported no cough is 17. The TOTAL number of people who reported no cough is 45. 17/45 = 37.777 = 38%