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%
