Find odd man out of the following series 15, 21, 63, 81, 69

Option d: 81. Solution: Let's analyze the numbers in the series 15, 21, 63, 81, 69 : - All the numbers are composite numbers divisible by 3 : 15 = 3 × 5 21 = 3 × 7 63 = 3 × 21 81 = 3 × 27 69 = 3 × 23 - However, 81 is a perfect square ( 81 = 92 ), whereas all the other numbers ( 15, 21, 63, 69 ) are not perfect squares. Therefore, 81 is the odd man out. Hence, Option D is the correct answer.

Find odd man out of the following series $15, 21, 63, 81, 69$

The correct answer is Option d: $81$. Let's analyze the numbers in the series $15, 21, 63, 81, 69$: - All the numbers are composite numbers divisible by $3$: $$15 = 3 \times 5$$ $$21 = 3 \times 7$$ $$63 = 3 \times 21$$ $$81 = 3 \times 27$$ $$69 = 3 \times 23$$ - However, $81$ is a perfect square ($81 = 9^2$), whereas all the other numbers ($15, 21, 63, 69$) are not perfect squares. Therefore, $81$ is the odd man out. Hence, **Option D** is the correct answer.

Number Series, Coding and DecodingMCQMTP Apr 21Question 2186 of 217

All Questions

Find odd man out of the following series $\displaystyle 15, 21, 63, 81, 69$

Options

\displaystyle 15

\displaystyle 21

\displaystyle 63

\displaystyle 81

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Correct Answer

✅ Option d — $\displaystyle 81$

All Options:

A $\displaystyle 15$
B $\displaystyle 21$
C $\displaystyle 63$
D $\displaystyle 81$

Detailed Solution & Explanation

Let's analyze the numbers in the series

\displaystyle 15, 21, 63, 81, 69

:
- All the numbers are composite numbers divisible by

\displaystyle 3

15 = 3 \times 5

21 = 3 \times 7

63 = 3 \times 21

81 = 3 \times 27

69 = 3 \times 23

- However,

\displaystyle 81

is a perfect square (

\displaystyle 81 = 9^2

), whereas all the other numbers (

\displaystyle 15, 21, 63, 69

) are not perfect squares.

Therefore,

\displaystyle 81

is the odd man out.

Hence, **Option D** 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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Find odd man out of the following series 15,21,63,81,69\displaystyle 15, 21, 63, 81, 6915,21,63,81,69