What is a Ratio?
Whatever we choose to compare can then be written as a ratio. There are three different forms.
A ratio can be written as a to b, a : b or
Here are some examples:
1.) 4 boys and 5 girls would be written as 4 to 5, 4 : 5 or
2.) 3 parts yellow and 4 parts blue would be written as 3 to 4, 3 : 4, or
Ratios can be parttopart, parttowhole, or wholetopart. Let's take a look at what this means.

When we compare boys to girls in a classroom, we are comparing part of the class to another part of the class. This would be a parttopart comparison.
When we compare boys to the whole class, this is a parttowhole comparison.
If we were to compare the class to the girls, this would be wholetopart comparison.
Given an example, we can actually write all the different types of ratios.
Example: A class is made up of 14 girls and 15 boys.
ParttoPart 14 : 15 shows girls to boys
ParttoWhole 14: 29 shows girls to the class
WholetoPart 29 : 14 shows the class to the girls
OR
ParttoPart 15:14 shows boys to girls
ParttoWhole 15 : 29 shows boys to the class
WholetoPart 29 : 15 shows the class to the boys
Example: A painter is mixing colors to get the right shade of green. He has used 4 parts blue for every 5 parts yellow.
ParttoPart 4: 5 shows blue to yellow
ParttoWhole 4 : 9 shows blue to the entire mixture
WholetoPart 9 : 4 shows the entire mixture to blue
OR
ParttoPart 5 : 4 shows yellow to blue
ParttoWhole 5 : 9 shows yellow to the entire mixture
WholetoPart 9 : 5 shows the entire mixture to yellow
The order that you write the ratio is important! 4 to 5 is not the same as 5 to 4.
Example:
1.) Write a ratio of triangles to squares. 4 : 7
2.) Write a ratio of squares to triangles.7 : 4
Notice that the order of the numbers depends on the order of what you want to compare.
3.) Write a ratio of triangles to total shapes.4 : 11
4.) Write a ratio of total shapes to triangles.11 : 4
Let's Review:
Ratios are used to compare two quantities. You can compare parts with parts or parts with the whole. When you write a ratio you have three choices for the form of your answer. You can write your answer as a : b, a to b or .
Related Links:
Math
What is a proportion?
Equivalent Ratios
Unit Rates
Ratios