If ... then ...
Cross out numbers using clues, draw conclusions from "if ... then ..." rules and build chains of reasoning.
- Russia: grade 3
Guide
In Russian schools (Grades 3-4, "Mathematical information") children reason with "if ... then ...", "so" and "therefore", and solve logic puzzles where every clue must be used.
A rule "if A then B" works one way: if A holds, B is true. But B does not give A. For example every number divisible by 10 is divisible by 5, but 15 is divisible by 5 and not by 10.
Puzzles with crossing out show how each clue removes some possibilities. Ask the child to make up a number riddle and test it on a friend.