Find the odd man out from the following series : $7, 23, 47, 119, 171, 287$.
Select Your Answer (Keyboard: A, B, C, D)
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Number Series, Coding and DecodingMCQPYQ Sep 24Question 2174 of 217
All Questions Correct Answer
✅ Option a — 171
All Options:
- A171
- B119
- C287
- D7
Detailed Solution & Explanation
Let's examine the mathematical pattern of the terms in the series: $7, 23, 47, 119, 171, 287p^2 - 2p$ is a consecutive prime number starting from $3p = 33^2 - 2 = 7p = 55^2 - 2 = 23p = 77^2 - 2 = 47p = 11\displaystyle : $11^2 - 2 = 119
- For : $13^2 - 2 = 167$ (the series lists $171$, which is incorrect)
- For : $17^2 - 2 = 287p^2 - 2$ using consecutive prime numbers holds perfectly for all terms except $171$, which should be $167$. Therefore, $171$ is the odd man out.
Hence, **Option A** is the correct answer.
- For : $13^2 - 2 = 167$ (the series lists $171$, which is incorrect)
- For : $17^2 - 2 = 287p^2 - 2$ using consecutive prime numbers holds perfectly for all terms except $171$, which should be $167$. Therefore, $171$ is the odd man out.
Hence, **Option A** 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 SyllabusExam Strategy Tip
This topic carries 5 Marks weightage. Focus on understanding core concepts rather than memorizing.
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