Number Series, Coding and DecodingPYQ May 25Question 4042 of 217
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Find the odd man out from the following: 445, 221, 109, 46, 25, 11, 4

Options

A25
B46
C109
D221
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Correct Answer

✅ Option b — 46

All Options:

  • A25
  • B46
  • C109
  • D221

Detailed Solution & Explanation

Let us analyze the pattern of the series from right to left (increasing order):
4,11,25,46,109,221,4454, 11, 25, 46, 109, 221, 445
Let\'s examine the relationship between consecutive terms Tk\displaystyle T_k and Tk−1\displaystyle T_{k-1} starting from 4\displaystyle 4:
- 4×2+3=11\displaystyle 4 \times 2 + 3 = 11
- 11×2+3=25\displaystyle 11 \times 2 + 3 = 25
- 25×2+3=53\displaystyle 25 \times 2 + 3 = 53 (but the term in the series is 46\displaystyle 46)

Let\'s check if the pattern continues using the expected value 53\displaystyle 53:
- 53×2+3=109\displaystyle 53 \times 2 + 3 = 109
- 109×2+3=221\displaystyle 109 \times 2 + 3 = 221
- 221×2+3=445\displaystyle 221 \times 2 + 3 = 445

All other terms fit the pattern Tn−1=2Tn+3\displaystyle T_{n-1} = 2 T_n + 3 (from right to left) perfectly. Thus, 46\displaystyle 46 is the odd term. It should have been 53\displaystyle 53.
Hence, **Option B** is the correct answer.

About This Chapter: Number Series, Coding and Decoding

Paper

Paper 3: Quantitative Aptitude

Weightage

5 Marks

Key Topics

Number series, Coding & Decoding, Odd man out

This chapter covers Number series, Coding & Decoding, Odd man out and is part of Paper 3: Quantitative Aptitude in the CA Foundation exam.

View Official ICAI Syllabus

Exam Strategy Tip

This topic carries 5 Marks weightage. Focus on understanding core concepts rather than memorizing.

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