Table of Contents

• Prequiz
• 1: Three tricks division can do
• Section 1: Ratios and Fractions
• 2: Finding Ratios
• 3: More uses for Ratios
• Section 2: Proportions and Percents
• 4: Proportions and Percents: Parts of the Whole
• 5: Absolute amounts from percents
• 6: Parts and wholes
• Section 3: Percent Change
• 7: Measuring how things change
• 8: Percent Change is not a direct comparison
• 9: Units, units, units
• Section 4: Biology
• 10: What's in your milk?
• 11: An experiment

More uses for Ratios

Often ratios are used to compare a part of a mixture to another part of a mixture. For example, classic pound cake is made with

• 1 pound butter
• 1 pound eggs
• 1 pound sugar
• 1 pound flour

The ratio of any two ingredients in this cake (say, sugar:butter) is 1:1. On the other hand, a "lowfat" pound cake has

• 12 oz corn-oil butter
• 10 oz eggs
• 13 oz flour
• 21 oz sugar

Now what is the ratio of sugar to butter?

What is the ratio of carb ingredients (sugar and flour) to fat ingredients (eggs and butter)?

Notice that I added some things up before doing the division. This is natural if I'm interested in categories of ingredients in the mixture.

In case you're missing the connections to biology here:

• blood is a mixture of components
• chemical reactions require (and produce) mixtures of molecules
• animals diets, and individual foods, consist of a mixture of nutrients

We'll get to some of these lovely examples later in the module.