Level 3: And, or, not, if

Logic and puzzles · level 3 of 8 · rough age 9-10 (a guide for parents; anyone can start anywhere)

In level 2 you sorted things with rules and solved puzzles by ticking and crossing. In this level you look closely at the four small words that hold every argument together: not, and, or and if. You use them to catch liars on an island, to write short computer programs with loops, to solve real 9-by-9 Sudoku, and to find a fake coin with only two weighings. Every lesson asks the same question: how can we be sure?

Lesson	You will be able to
Not, and, or	Decide when an and or an or sentence is true, and write the opposite of a sentence correctly
If ... then	Say when an if ... then sentence is broken, and explain why "the ground is wet" does not prove it rained
Knights and knaves	Solve truth-teller and liar puzzles by trying both cases and crossing off the impossible one
Coding with loops	Use repeat to draw shapes with short code, find the pattern that shortens code, and put a loop inside a loop
9-by-9 Sudoku moves	Use the "only place" and "only number" moves, and explain why a good puzzle has exactly one answer
Weighing puzzles	Find one heavy coin among 9 with two weighings, and explain why splitting into threes is the secret

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