Ratios and Equivalent Ratios

Ratios - a comparison of two numbers or quantities measured in the same units. 

For instance I could describe the number of boys to girls in the class for every 1 boy there are 2 girls

1:2 so if there are 12 boys how many girls are there? The top row represents boys and the bottom row represents girls, how many girls are there if there are 12 boys?

We can find the number of girls by finding the equivalent ratios.