To make your weekend pancakes, you had to combine pancake mix and water together in very specific amounts. When you needed to make more pancakes than usual, you had to increase the amounts of all the ingredients—in equal amounts. To figure out how much mix and water to use, you probably considered the amount of pancake mix needed compared to the amount of water. If that was your approach, you were using a ratio. A ratio is a comparison between two different amounts or numbers—the amount of pancake mix compared to the amount of water, for instance.

You also use ratios when you compare the number of boys to the number of girls in your classroom, or the number of passing grades to failing grades on a test. If you hear someone say, "At my school, boys outnumber girls two to one," that student is using a ratio to compare numbers.

How do you express a ratio in writing? Let's look back at our pancake batter for an example. We know that we needed four cups of mix and three cups of water. There are three ways that you can write the ratio of pancake mix to water—each method is demonstrated on one of the slides below.

Using Words The ratio of pancake mix to water can be expressed using words. You can write this ratio as "four to three." Odds Notation You can also write ratios using odds notations and a colon. The ratio of pancake mix to water is then written as 4:3. Fraction Notation You can even use fractions to express ratios. The ratio of pancake mix to water is written as \(\mathsf{ \frac{4}{3} }\).