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

Three tricks division can do

Frequently, in these modules and in your biology classes, you will be asked to make a variety of calculations involving division. No, we're not going to go into doing long division -- you do get to keep your calculator. However, division is still a rather tricky subject, and one that often gets students in trouble. The question is:

What gets divided by what?

Luckily, there's a very simple answer:

It depends.

Specifically, it depends on what you're trying to do with the division. But there are a number of "flavors" of division that I list below -- most of the time, what you're trying to do will fall into one of them.

1. Ratios
2. Percent, Proportion, or Probability
3. Percent Change

We'll go through each of these options. By the end, you should feel confident making a given calculation without consulting your instructor -- and you should also feel confident choosing which calculation fits a given situation.