Directions
No matter how much orange juice we make, we still need 3 cups of water for every 1 cup of concentrate. So the ratio of 12 cups of water to 4 cups concentrate in the quadrupled recipe is the same as the ratio of concentrate to water in the original recipe.
In other words, the relationship between the two terms in the ratio 3:1 is the same as that in 12:4. Just do the math! 3 is three times as much as 1, and 12 is three times as much as 4. Since 3:1 and 12:4 have the same relationship, these two ratios are equal.
When two ratios are equal, we say they are in proportion. In other words, a proportion is a mathematical statement that two ratios are equal.
We write proportions like this:
3 to 1 equals 12 to 4
3:1 = 12:4
3/1 = 12/4