Number Series – Quick‑Start Study Notes
(For the NMMS Mental Ability Test – MAT)
1. What is a “Number Series”?
- A list of numbers that follows a hidden rule.
- The missing number is the one that keeps the rule true for all entries.
Analogy:
Think of a recipe that uses the same pattern of ingredients each time. If you know the pattern, you can predict the next ingredient.
2. Simple Rules to Look For
| Rule | Everyday Analogy | Tiny Example |
|---|---|---|
| Add/Subtract a constant | Adding the same amount of sugar each cup | 2, 5, 8, 11 → +3 each step |
| Multiply/Divide by a constant | Doubling a bead chain | 3, 6, 12, 24 → ×2 each step |
| Alternating pattern | Switching between two colors in a scarf | 1, 4, 2, 5, 3, 6 (odd vs. even) |
| Reversing digits | Mirror‑writing a word | 12, 21, 13, 31 → flip digits |
| Square / Cube pattern | Building blocks that grow by 1², 2², 3²… | 1, 4, 9, 16 → +3, +5, +7 (squares) |
| Cumulative sum | Adding all previous steps together | 1, 1, 2, 4, 8 → each = sum of all before |
3. Step‑by‑Step Approach
- Write down the series clearly.
- Check the difference between consecutive numbers.
- Same difference → Add/Subtract rule.
- Check the ratio (divide each by its predecessor).
- Same ratio → Multiply/Divide rule.
- Look for alternation (two different numbers repeating).
- Try small operations (add 1, subtract 2, multiply 3).
- If still stuck, try reversing digits or summing previous numbers.
Tip: If the series looks messy, try plugging in n (the position) into a simple formula.
4. Quick Practice Checklist
- Identify constant difference?
- Identify constant ratio?
- Spot two alternating patterns?
- Check for digit reversal?
- Sum of previous numbers?
If 3 or more boxes are checked, your rule is probably correct.
5. Tiny Example (Complete Walk‑through)
Series: 3, 6, 12, 24, ?
- Check differences: 3→6 (+3), 6→12 (+6), 12→24 (+12).
- Differences are doubling each time.
- What happens next? The difference after +12 should be +24.
- Add to last number: 24 + 24 = 48.
Answer: 48
6. Final Thought
Treat each number series like a pattern in a song. If you hear the beat (rule), you can predict the next note (number). Practice a few times, and the rhythm will become second nature. Happy studying!