Quick Concept Summary
Number-series problems are pattern-recognition questions. A good solver checks simple patterns first before hunting for exotic ones.
Pattern Checklist
| Pattern | Example |
|---|---|
| Constant difference | 4, 9, 14, 19 |
| Growing difference | 2, 5, 10, 17 |
| Multiplication | 3, 6, 12, 24 |
| Squares | 1, 4, 9, 16 |
| Alternating | 2, 5, 4, 10, 8, 20 |
Worked Examples
Example 1
Find the next term: 7, 12, 17, 22, ?
Difference is +5, so the answer is 27.
Example 2
Find the next term: 2, 6, 12, 20, 30, ?
These are 1x2, 2x3, 3x4, 4x5, 5x6, so next is 6x7 = 42.
Example 3
Find the next term: 3, 6, 5, 10, 9, 18, ?
The pattern alternates x2, -1, so next is 17.
Practice Questions
1. 5, 11, 19, 29, ? 2. 1, 8, 27, 64, ? 3. 4, 8, 7, 14, 13, ? 4. 2, 3, 5, 8, 12, ?
Common Mistakes
- Testing a complicated rule before checking differences
- Ignoring alternating positions
- Treating one lucky match as a complete pattern