Unit 3 · Counting

Chapter 3.1

Multiply or Add?

Most counting mistakes are not arithmetic errors: they multiply where they should add, or add where they should multiply.

lesson 13 of 42

By the end

  1. 01Multiply when choices happen in sequence, add when cases are separate
  2. 02Split a count into cases that neither overlap nor leave anything out
  3. 03Fill the most constrained position first

In unit 3

  1. 3.1Multiply or Add?
  2. 3.2Count What You Don't Want
  3. 3.3Arrangements and Overcounting
  4. 3.4Choosing, Pascal, and Stars and Bars
  5. 3.5Counting Two Ways
  6. 3.6Too Few Boxes
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