Category
Logic
Quantifiers, contrapositives, and arguments that hold up.
Logic is the grammar of proof. Every other category leans on it, and it is worth practising on its own, where the reasoning is the entire content of the problem rather than the scaffolding around it.
You will find propositional and predicate logic, negation and contraposition, quantifier order, truth tables, and puzzles about consistent and inconsistent statements. Precision matters more than speed here.
Latest problems
40 problems
Pigeonhole Birthdays
1167
5
Contrapositive of a nested conditional
1000
5
Counting Down Then Up
1000
6
Negating a statement
1000
3
Counting the Days Between
1000
7
Knights, knaves, and one claim
1000
5
Largest Value Making an Expression Prime
917
4
Only some, not all
717
3