Key facts & rules

• A prime number has exactly 2 factors: 1 and itself. 1 is NOT prime.
• HCF: highest common factor — use a Venn diagram of prime factors.
• LCM: lowest common multiple — product of all prime factors, using highest powers.
• Standard form: A × 10ⁿ where 1 ≤ A < 10.
• Rational numbers can be written as fractions p/q (q ≠ 0). Irrational numbers cannot (e.g. π, √2).
• To convert a recurring decimal to a fraction: multiply by 10ⁿ to eliminate the recurring part, then subtract.
• Index laws: aᵐ × aⁿ = aᵐ⁺ⁿ; aᵐ ÷ aⁿ = aᵐ⁻ⁿ; (aᵐ)ⁿ = aᵐⁿ; a⁰ = 1; a⁻ⁿ = 1/aⁿ; a^(1/n) = ⁿ√a.