Ratio of 200 students to 20 books:
= 200:20 or (in fraction form)
We already have the ratio which is 200:20 but we should reduce it for it is a must.
200:20 (divide 10 to both sides)
= 20:2 (divide 2 to both sides)
= 10:1 (cannot be divided by a common factor anymore)
Therefore the ratio of 200 students to 20 books is 10:1.