Number Properties & Operations Number Types Natural numbers: 1, 2, 3, ... Whole numbers: 0, 1, 2, 3, ... Integers: ..., -2, -1, 0, 1, 2, ... Rational numbers: can be expressed as a/b (includes fractions, terminating/repeating decimals) Irrational numbers: cannot be expressed as a/b (π, √2, etc.) Key Properties Order of operations: PEMDAS Absolute value: distance from zero, always non-negative Divisibility rules: quick tests for 2, 3, 5, 9, 10 Prime factorization: break into prime factors ACT Tips GCF and LCM questions are common Know your perfect squares up to 15² Understand even/odd rules for +, -, ×