Unit 11 · Sets
Introduction to Sets
Mathematics · Grade 7
What You Will Be Able To Do
✅Tell whether a description is well defined, and sharpen it if it is not
{ }Write sets correctly using brackets, commas and the membership symbols
🔢State n(A), and distinguish equal sets from merely equivalent ones
🧮List every subset of a small set and predict how many there will be
“
The tall students in this class is not a set, because two teachers would draw the line in different places and neither would be wrong.
Presenter notes: Open with a disagreement rather than a definition. Ask every student who thinks they are tall to stand up, then ask the class whether the right people are standing. There will be argument, and that argument is the lesson. Now ask everyone over 150 cm to stand and measure two of the borderline cases with a tape. Nobody argues this time. Say that mathematics can only work with the second kind of collection, and that the first kind, however sensible it sounds, is useless to it.