First, find what are the numbers that can be divided to 10 and 85. The numbers 10 and 85 can be divided by 5. 10 divided by 5 is equals to 2 and 85 divided by 5 is equals to 17. Ratio is just like a fraction, you need to reduce its terms if you need to. Let’s say 10:85 is a fraction and since it is obvious that it can be divided by 5, you just need to reduce its term. 10/85 can be reduced into 2/17 which is just the same with ratios 10:85 is equals to 2:17.