General Test — Number series

Overview

Series questions ask for the next or missing term. Most follow one of a few patterns.

Key concepts

• Differences: check the gaps between terms, then the gaps between gaps.
• Multiplication: ×2, ×3, often with +1 or −1 (3, 7, 15, 31 → ×2 + 1).
• Squares and cubes: 1, 4, 9, 16 or 1, 8, 27, 64.
• Primes: 2, 3, 5, 7, 11, 13.

Important points

• If differences grow fast, try multiplication instead of addition.
• For odd-one-out questions, check whether all but one share a property such as being prime.

Quick revision

Differences first, then ratios, then squares, cubes and primes.