A ratio is a comparison of two numbers. It can be written with a colon ( ), or using the word "to" ( to ), or as a fraction:
Write the ratio of blue dots to red dots in the figure.
There are blue dots and red dots.
Write the ratio as a fraction.
Now reduce the fraction .
So the ratio of blue dots to red dots is .
(Note that the ratio of red dots to blue dots is the reciprocal : or .)