A ratio is how much of one object is there related to the other object. It is a division.
For example:
The ratio between an object A and an object B is:
A/B
The ratio between an object B and an object A is:
B/A
Real example:
Last NFL season
Buffalo Bills 10 wins
New York Jets 7 wins
Ratio between the Bills wins and Jets wins
10/7
Ratio between the Jets wins and Bills wins
7/10
