Wrong Number Series for Banking Exams | Concepts, Patterns & Short Tricks | Part 2

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In Banking Exams (IBPS PO/Clerk, SBI PO/Clerk, RRB PO/Clerk), Wrong Number Series is a regular and critical question type in the Quantitative Aptitude section.

बैंकिंग परीक्षाओं के Quantitative Aptitude सेक्शन में Wrong Number Series (गलत संख्या श्रृंखला) एक महत्वपूर्ण टॉपिक है, जिसमें सही अप्रोच और सटीक गणना की आवश्यकता होती है।

This master guide covers practical elimination techniques, structural pattern identification, and exam-standard practice questions.

Banking Quantitative Aptitude — Part 2

Wrong Number Series: Rules, Tricks & Practice Questions

गलत संख्या श्रृंखला: नियम, शॉर्टकट एवं अभ्यास प्रश्न (Bilingual Edition)

🎯 4 Golden Rules to Spot the Wrong Term / गलत पद पहचानने के नियम

1. Two-Difference Distortion Rule

English: For a wrong term appearing in the middle of a difference-based series, the two consecutive differences around it are usually affected.

हिंदी: यदि गलत पद श्रृंखला के बीच में हो, तो उसके दोनों ओर के दो क्रमागत अंतर (differences) सामान्यतः प्रभावित होते हैं।

2. Start from the Simplest Terms

English: Begin verifying the pattern from the portion of the sequence where the numbers are easiest to calculate and the underlying logic is most transparent.

हिंदी: पैटर्न की पुष्टि श्रृंखला के उस भाग से शुरू करें जहां संख्याएं सरल हों और गणना सबसे तेज हो सके।

3. Multiplicative Boundary Check

English: In rapidly increasing sequences, test the approximate ratio (T_n ≈ T_n-1 × k) across terms to spot where the progression breaks.

हिंदी: तेजी से बढ़ती श्रृंखला में अनुमानित गुणांक अनुपात (T_n ≈ T_n-1 × k) चेक करें जिससे विचलित पद तुरंत पकड़ में आ सके।

4. Base Series Replacement

English: Once a suspicious term is located, substitute the mathematically expected value and check whether it produces the remaining sequence correctly.

हिंदी: जिस पद पर संदेह हो, उसकी जगह सही संख्या रखकर देखें कि क्या आगे की श्रृंखला सही बन रही है।

⚡ High-Frequency Exam Patterns / प्रमुख पैटर्न

Pattern 1: Distorted Difference Series (अंतर आधारित त्रुटि)

32,   34,   37,   46,   62,   87,   123

Solution Breakdown / समाधान:

• Actual Differences: +2, +3, +9, +16, +25, +36
• Expected Squares Pattern: 1², 2², 3², 4², 5², 6² (+1, +4, +9, +16, +25, +36)
• Discrepancy: 32 + 1² = 33, but the given 2nd term is 34, which disturbs the +1 and +4 differences into +2 and +3
• Wrong Term (गलत पद): 34 (Correct value: 33)

Pattern 2: Multiplicative Series with Step-up Squares (×n + k²)

15,   19,   47,   155,   653,   3301

Solution Breakdown / समाधान:

• 15 × 1 + 2² = 15 + 4 = 19
• 19 × 2 + 3² = 38 + 9 = 47
• 47 × 3 + 4² = 141 + 16 = 157 (Given value is 155)
• Verification: 157 × 4 + 5² = 628 + 25 = 653 (Matches subsequent term)
• Wrong Term (गलत पद): 155 (Correct value: 157)

Pattern 3: Constant Multiplier with Step-up Addition (×3 + n)

3,   10,   32,   100,   301,   908

Solution Breakdown / समाधान:

• 3 × 3 + 1 = 10
• 10 × 3 + 2 = 32
• 32 × 3 + 3 = 96 + 3 = 99 (Given value is 100)
• Verification: 99 × 3 + 4 = 297 + 4 = 301 (Matches)
• Verification: 301 × 3 + 5 = 903 + 5 = 908 (Matches)
• Wrong Term (गलत पद): 100 (Correct value: 99)

Pattern 4: Halving with Constant Subtraction ((T_n-1 − c) ÷ 2)

446,   222,   110,   54,   24,   12

Solution Breakdown / समाधान:

• (446 − 2) ÷ 2 = 222
• (222 − 2) ÷ 2 = 110
• (110 − 2) ÷ 2 = 54
• (54 − 2) ÷ 2 = 26 (Given value is 24)
• Verification: (26 − 2) ÷ 2 = 12 (Matches final term)
• Wrong Term (गलत पद): 24 (Correct value: 26)

📝 Practice Questions (Banking Exam Standard) / अभ्यास प्रश्न

Q1. 5,   10,   17,   24,   37,   50,   65

Pattern: n² + 1 series (2²+1=5, 3²+1=10, 4²+1=17, 5²+1=26, 6²+1=37, 7²+1=50, 8²+1=65)
Wrong Term: 24 (Correct value: 26)

Q2. 850,   843,   829,   808,   788,   745,   703

Pattern: Differences are consecutive multiples of 7 (−7, −14, −21, −28, −35, −42)
Check: 808 − 28 = 780 (Given 788; 780 − 35 = 745)
Wrong Term: 788 (Correct value: 780)

Q3. 16,   17,   20,   29,   56,   136

Pattern: Differences are powers of 3 (+3⁰, +3¹, +3², +3³, +3⁴ = +1, +3, +9, +27, +81)
Check: 16+1=17, 17+3=20, 20+9=29, 29+27=56, 56+81=137 (Given is 136)
Wrong Term: 136 (Correct value: 137)

Q4. 1,   3,   10,   36,   152,   760,   4632

Pattern: ×1 + 2, ×2 + 4, ×3 + 6, ×4 + 8, ×5 + 10, ×6 + 12
Check: 152 × 5 + 10 = 760 + 10 = 770 (Given 760; 770 × 6 + 12 = 4632)
Wrong Term: 760 (Correct value: 770)

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