12 students play defense. 1st step. 6/9 of 27 is 18. 2nd. the ratio of the students playing offense to the total number of students playing soccer is 1 to 3 which means the total amount of students is '3', in the ratio it's 3 because it's simplified (i like to think of it as 'groups'). since we know that there are a total of 18 students and there's 3 total 'groups' we divide 18 into 3 which is 6. so there's 6 students in each group. we subtract 6 (1 group) from 18 ( the total number of students) which is 12, so there are 12 students playing defense. if you wrote the ratio again without simplifying it would be 6:18