What is the ratio between 100 and 0? 100? undefined?

Question

As the title of the topic says, what is the ratio between 100 and 0? In this case, 100 and 0 represent 100% and 0%. A friend of mine says that it is equal to 100 because there is no other case in which it can be equal to 100, and in that case it would mean that for each element in set A there is no element in set B. I tend to believe that it is undefined, because there is a case in which the ratio is almost equal to 100, which is the ratio between 99,01% and 0,99%. Could this issue be seen as a matter of interpretation of the meaning of the ratio, or is there something that we have not considered?