Explanation:
x is some unknown number such that
17x = number of students
3x = number of faculty
17x+3x = 20x = 400 = total number of people
20x = 400 solves to x = 20
Therefore,
17x = 17*20 = 340 students
3x = 3*20 = 60 faculty
The ratio 340:60 reduces to 17:3 after dividing both parts by the GCF 20