Ratios
A ratio is a comparison of two numbers. It can be written with a colon (1:5), or using the word “to” (1 to 5), or as a fraction: 
Example:
Write the ratio of blue dots to red dots in the figure.
There are 6 blue dots and 4 red dots.
Write the ratio as a fraction.
Now reduce the fraction.
So the ratio of blue dots to red dots is 3:2.
(Note that the ratio of red dots to blue dots is the reciprocal: 
or 2:3.)
