# Odd man out series - Aptitude test, questions, shortcuts, solved example videos ## Odd man out and series

This topic depends upon all basic concepts we have studied till now in this aptitude session. Numbers, A.P./G.P., Squares and cube roots, binomial theorem, etc.

Being logical and increasing your intelligence will help in solving the problems of odd man out and series. Your perspective in solving these types of problems should be unique. Different problems related to alphabets, numbers, metals, etc can be asked, hence different rules, differences should be figured out quickly to solve because time is limited.

Quick Tips and Tricks

Series:
The terms or elements follow a definite law in series but it cannot be generalized. You should know, what is the definite relationship between numbers which make the set of given terms in series. Addition, subtraction, multiplication, division, transposition of terms and series generally form such series. The different questions asked may depend upon the following:

1) Odd number/Even number/Prime numbers
The series may consist of odd numbers /even numbers or prime numbers except one number, which will be the odd man out. Hence, before solving numerical on this topic must revise all basic concepts.

2) Perfect squares/Cubes:
Squares: 9, 16, 49, 81 ….
Cubes: 27, 64, 125, 216 ….

3) Multiple of numbers:
The series contains numbers which are multiple of different numbers.
Example: 4, 8, 12, 16, 20…..

4) Numbers in A.P./G.P.
Geometric progression: x, xr, xr3, xr4
Arithmetic progression: x, x + y, x + 2y, x + 3y are said to be in A.P.
The terms in series may be arithmetic or geometric progression.

5) Difference or sum of numbers:
The difference between two consecutive numbers may increase or decrease

6) Cumulative series:
In this type, the third number is the addition of previous two numbers.
Example: 2, 4, 6, 10, 16, 26 ……

7) Power series:
In this type, the terms are defined on the basis of powers of numbers; the number may be expressed in the form of n3 – n.
Example:
If n = 4, n3 – n = 60
If n = 5, n3 – n = 120…
Series: 60, 120, 210, 336 …

8) The middle digit is the sum of other two digits.
Example: 165, 121, etc

9) The series of numbers may follow different sequence as shown below:
(n2 – 1), (n2 + 1), (n2 – n), (n3 – n), (n2 – n + 1), (n2 – n – 1), etc

a) If numbers in the series are 1,5, 11, 19, 29…. then the relation is (n2 – n – 1)

b) If numbers in the series are 21, 31, 43 then the relation is (n2 – n + 1)
Example:
If n = 5, (52 – 5 + 1) = 21
If n = 6, (62 – 6 + 1) = 31
If n = 7, (72 – 7 + 1) = 43

Types of questions

Type 1: Find the missing number

Q 1. 8, 16, 32, 64, 128, 256, ___, 1024

a. 423
b. 512
c. 896
d. 980
View solution

Correct Option: (b)

Hint: Each preceding number is multiplied by 2
8 × 2 = 16, 16 × 2 = 32, 32 × 2 = 64, 64 × 2 = 128, 256 × 2 = 512 and 512 × 2 = 1024
Hence, the missing number is 512

Q 2. 11, 13, 17, 19, 23, 29, _____

a. 31
b. 33
c. 51
d. None of the above
View solution

Correct Option: (a)

Hint: Numbers 11, 13, 17, 19, 23 and 29 are all prime numbers.
Therefore, next prime number is 31

Q 3. 15, 33, 69, 141, ___, 573, 1149

a. 151
b. 169
c. 285
d. 456
View solution

Correct Option: (c)

Hint:
Each number is twice the previous number with 3 added to the answer.

15 × 2 = 30, 30 + 3 = 33
33 × 2 = 66, 66 + 3 = 69
69 × 2 = 138, 138 + 3 = 141
141 × 2 = 282, 282 + 3 = 285
285 × 2 = 570, 570 + 3 = 573
573 × 2 = 1146, 1146 + 3 = 1149
Hence, the missing number is 285

Q 4. 6, 24, ___ , 120, 210, 336

a. 36
b. 60
c. 72
d. 95
View solution

Correct Option: (b)

Hint:
Power series: n3 – n
23 – 2 = 6
33 – 3 = 24
43 – 4 = 60
53 – 5 = 120
63 – 6 = 210
73 – 7 = 336
Hence, the missing number is 60

Type 2: Find/Pick the odd man out

Q 5. 9, 16, 25, 36, 125, 169, 196, 225

a. 36
b. 196
c. 169
d. 125
View solution

Correct Option: (d)

Hint:
All numbers except 125 are perfect squares.
53 = 125
Hence, the odd number is 125

Q 6. 121, 275, 396, 385, 891, 932

a. 275
b. 396
c. 891
d. 932
View solution

Correct Option: (d)

Hint:
The middle digit is the sum of other two digits.
121, 275, 396, 385, 891 all these numbers have middle digit as the sum of other two digits.

Q 7. 3, 5, 7, 14, 17, 19

a. 3
b. 7
c. 14
d. 17
View solution

Correct Option: (c)

Hint:
All numbers except 14 are prime numbers.
Hence, the odd number is 14.

Type 3: Find the wrong number

Q 8. 6, 9, 11, 12, 14, 15, 25

a. 9
b. 11
c. 14
d. 25
View solution

Correct Option: (b)

Hint:
Each number is composite except 11
Hence, the odd number is 11

Q 9. 9, 12, 17, 20, 25, 28, 34, 36, 41

a. 25
b. 28
c. 34
d. 41
View solution

Correct Option: (c)

Hint:
Here, the differences between two successive numbers from the beginning are 3, 5, 3, 5…
34 is the wrong term because the next number should have the difference of 5 i.e. the number should be 33.
Hence, the odd number is 34

Q 10. 34, 105, 424, 2123, 12756

a. 12756
b. 2123
c. 424
d. 34
View solution

Correct Option: (b)

Hint:
34 × 3 = 102, but here the next number is 105.
Hence, 102 + 3 = 105

Try this concept for next numbers in sequence.
105 × 4 = 420, 420 + 4 = 424
It’s working! Check all the numbers in series
424 × 5 = 2120, 2120 + 5 = 2125
2125 × 6 = 12750, 12750 + 6 = 12756

Hence, correct answer is 2123. The term after 424 should be 2125 instead of 2123.

Q 11. 6, 12, 20, 30, 42, 54, 72, 90, 110

a. 20
b. 42
c. 54
d. 90
View solution

Correct Option: (c)

Hint:
2 × 3 = 6, 3 × 4 = 12, 4 × 5 = 20, 5 × 6 = 30, 6 × 7 = 42, 7 × 8 = 56, 8 × 9 = 72
The numbers in the series are in order as shown above.
After 42, the next number in series should be 56 instead of 54.
Hence, the odd number is 54

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