Number Series — Banking Reasoning Notes Ch. 7

Introduction

Number Series appears in both the Quant and Reasoning sections of bank exams — the underlying pattern logic is identical, but reasoning-section series tend to be shorter and reward speed over deep calculation. For the full pattern-type breakdown and worked formulas, see the dedicated Quantitative Aptitude Number Series chapter; this page focuses on the fast-recognition habits useful specifically in the reasoning section.

Quick Pattern Checklist

Check	What to Look For
1. Constant difference	Same number added/subtracted each step
2. Constant ratio	Same number multiplied/divided each step
3. Difference-of-differences	Differences themselves increase/decrease steadily
4. Squares/cubes	Terms match n², n³, or n²±k patterns
5. Alternating terms	Odd and even positions follow two separate simple rules

Q. Find the missing number: 5, 11, 23, 47, ?

Each term = previous×2 + 1. Check: 5×2+1=11, 11×2+1=23, 23×2+1=47. Next = 47×2+1 = 95.

Q. Find the wrong number: 3, 8, 15, 24, 36, 48

Differences: 5, 7, 9, then should be 11, giving 24+11=35, not 36. Pattern is n²+2: 1+2=3, 4+2=... check via differences confirms next should be 35. So 36 is wrong; correct value is 35.

⚠️ Key Insight: In the reasoning section, series questions are almost always solvable within the first two checks (constant difference or ratio) — if neither works within 10 seconds, move on and return later rather than spending excess time here.

✅ Practice Focus: Fast difference/ratio recognition · Square-cube pattern spotting · Time-boxing this question type to protect time for puzzle-heavy questions.

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