Number Series - Solved Questions and Answers

Last Updated : 23 Jul, 2025

A number series is an ordered sequence of numbers following a specific pattern or rule. These patterns can involve addition, multiplication, or more complex mathematical relationships. Number series are used to develop logical thinking and appear in math problems, puzzles, and aptitude tests.

Number Series questions and answers are provided below for you to learn and practice.

Question 1: Find what number would come in place of the question mark(?).

Series: 2, 5, 12.5, ?, 78.125, 195.3125

a) 31.25

b) 40.25

c) 32.50

d) 21.00

Solution:  (a) 31.25

Explanation:
If you observe the pattern, then you can see
2 × 2.5 = 5
5 × 2.5 = 12.5
12.5 × 2.5 = 31.25
31.25 × 2.5 = 78.125
78.125 × 2.5 = 195.3125
Hence, the correct answer is 31.25

Question 2: Find what number would come in place of the question mark(?).

Series: 50, 45, 40, 35, 30, ?

a) 28

b) 15

c) 25

d) 20

Solution:  (c) 25

Explanation:
If you observe the pattern, then you will see, it's nothing but constant difference series.
50 - 5 = 45
45 - 5 = 40
40 - 5 = 35
35 - 5 = 30
30 - 5 = 25
Hence, the correct answer is 25.

Question 3: Find what number would come in place of the question mark(?).

Series: -10, -8, 6, 40, 102, ?

a) 105

b) 200

c) 216

d) 129

Solution: (b) 200

Explanation:
Observing patterns carefully you will find that this question belongs to the category of square series.
-10 + ( 2²- 2 ) = -8
-8 + ( 4²- 2 ) = 6
6 + ( 6²- 2 ) = 40
40 + ( 8²- 2 ) = 102
102 + ( 10²- 2 ) = 200
Hence, the correct answer is 200.

Question 4: Find what number would come in place of the question mark(?).

Series: 25, 49, 121, 169,?

a) 225

b) 256

c) 289

d) 361

Solution: (c) 289

Explanation:
Observing patterns carefully, you will observe that, this series is based on two concepts one is squares and the other is a prime number.
5² = 25
7² = 49
11²= 121
13² = 169
17² = 289
Hence, the correct answer is 289

Question 5: Find what number would come in place of the question mark(?).

Series: 1, 30, 5, 26, 9, 22, 13, 18, ?

a) 17

b) 22

c) 28

d) 19

Solution: (a)  17

Explanation:
Observing the pattern carefully, you will observe that, this series consist of 2 different series.
Let me point out them for ease of understanding ---
1 + 4 = 5
5 + 4 = 9
9 + 4 = 13
13+4= 17.
Similarly,
30 - 4 = 26
26 - 4 = 22
22 - 4 =18

Question 6: Find the number that will come in the place of the question mark.

Series: 4, 18, ?, 100, 180, 294, 448.

a) 62

b) 86

c) 38

d) 48

Solution: (d)  48

Explanation:
Observing pattern carefully you will find that this question belongs to the category of squares and cube series.
2³ – 2² = 8 – 4 = 4
3³ – 3² = 27 – 9 = 18
4³ – 4² = 64 – 16 = 48
5³ – 5² = 125 – 25 = 100
6³ – 6² = 216 – 36 = 180
7³ – 7² = 343 – 49 = 294
8³ – 8² = 512 – 64 = 448
Hence 48 would be our answer, as it is the number that would come in place of a question mark.

Question 7: Find the number that will come in the place of the question mark.

Series: 11, 12, 15, 20, 27, ?

a) 36

b) 35

c) 38

d) 41

Solution: (a) 36

Explanation:
Here, the series follows a pattern of the sum of consecutive odd numbers.
11 + 1 = 12
12 + 3 = 15
15 + 5 = 20
20 + 7 = 27
27 + 9 = 36.
Hence, the missing number would be 36.

Question 8: Find the number that will come in the place of the question mark.

Series: 14, 25, 47, 91, 179, ?.

a) 255

b) 321

c) 355

d) 211

Solution:  (c) 355

Explanation:
observing the pattern we get that the difference between consecutive terms is being doubled every time.
25 – 14 = 11
47 – 25 = 22
91 – 47 = 44
179 – 91 = 88
So, if 88 is doubled, we get 176.
Hence, 179 + 176 = 355
Hence the missing term is 355.

Question 9: Find the number that will come in the place of the question mark.

Series: 4, 6, 9, 14, 21, ?.

a) 28

b) 32

c) 34

d) 40

Solution: (b) 32

Explanation:
Observing the pattern, one can easily come to know that, the difference between consecutive terms is a prime number.
4 + 2 = 6
6 + 3 = 9
9 + 5 = 14
14 + 7 = 21
21 + 11 = 32.
Hence, the missing number will be 32.

Question 10: Find the number which would come in place of question marks.

Series: 3, 4, 7, 8, 11, 12, ?, ?.

a) 13, 14

b) 18, 20

c) 15, 16

d) 19, 20

Solution: (c) 15, 16

Explanation:
This is a Hybrid series, which is formed from the combination of two series i.e 3,7,11,.... and 4,8, 12.
So, the difference between every term in different series is 4. hence 11 + 4 would be the next term i.e 15
and 12 + 4 =16 is the further next term.

Question 11: Find the number which is wrong.

Series: 2, 3, 12, 37, 86, 166, 288.

a) 2

b) 12

c) 37

d) 166

Solution: (d) 166

Explanation:
Observing the pattern carefully, every term is formed from a sum of (the previous term and consecutive odd number squares).
2 + 1² = 2 + 1 = 3
3 + 3² = 3 + 9 = 12
12 + 5² = 12 + 25 = 37
37 + 7² = 37 + 49 = 86
86 + 9² = 86 + 81 = 167
167 + 11² = 167 + 121 = 288.
Clearly, we can see that 167 should be there instead of 166. Hence 166 is the wrong term.

Question 12: Find the number which would come in place of question mark.

Series: 81 : 101 :: 121 : ? .

a) 141

b) 143

c) 170

d) 145

Solution: (d) 145

Explanation:
Here 81 is nothing but 9² and 101 is nothing but (9 + 1)² +1
So, likewise this
121 is nothing but 11²
so ,next term will be (11 + 1)² + 1 = 145

Question 13: Find the number which would come in place of question mark.

Series: 11 : 121 :: 15 : ?

a) 169

b) 196

c) 225

d) 256

Solution: (c) 225

Explanation:
Observing pattern we get,
Here, 11² = 121
So, 15²= 225
So, the missing number is 225.

Question 14: Find the number which would come in place of question mark.

Series: 2, 4, 8, 10, 14, ?.

a) 16

b) 18

c) 24

d) 20

Solution: (a) 16

Explanation:
This series is an alternating series, where a pattern following is +2, +4, +2, +4, and so on
2 + 2 = 4
4 + 4 = 8
8 + 2 = 10
10 + 4 = 14
14 + 2 = 16
Hence the next term will be 16.

Question 15: Find the number which would come in place of question mark.

Series: 1, 8, 9, 64, ?.

a) 27

b) 49

c) 25

d) 64

Solution: (c)  25

Explanation:
Observing carefully one can come to know that this series is nothing but squares and cubes of numbers starting from 1
1² = 1
2³ = 8
3² = 9
4³ = 64
5² = 25
Hence, 25 will be the answer.

Question 16: Find the number which would come in place of question mark.

Series: 6, 11, 18, 27, ?.

a) 33

b) 40

c) 38

d) 81

Solution:  (c)  38

Explanation:
Here, every term is squares from (starting from 2 ) with the addition of 2.
2² + 2 = 6
3² + 2 =11
4² + 2 = 18
5² + 2 = 27
6² + 2 = 38

Question 17: Find the number which would come in place of question mark.

Series: 3, 4.5, 9, ?

a) 22.5

b) 18

c) 13.5

d) 27

Solution:  (a)  22.5

Explanation:
This series is a product based, below is the pattern for finding the next term
3 × 1 = 3
3 × 1.5 = 4.5
4.5 × 2 = 9
9 × 2.5 = 22.5
Hence, 22.5 will be our answer.

Question 18: Find the number which would come in place of question mark.

Series: 3, 5, 7, 9, 11, ?,

a) 13

b) 17

c) 19

d) 12

Solution: (a) 13

Explanation:
It can be seen in 2 ways,
1. it is simple just a difference of 2 in every consecutive term that is --
3 + 2 = 5
5 + 2 = 7
7 + 2 = 9
9 + 2 = 11
11 + 2 = 13. Hence 13 will be the answer.
2. It can also be seen as a difference of squares of numbers -
2² - 1² = 3
3² - 2² = 5
4² - 3² = 7
5² - 4² = 9
6² - 5² = 11
7² - 6² = 13. Hence 13, will be the answer.

Question 19: Find the number which would come in place of question mark.

Series: 1, 7, 37, 187, 937, ?.

a) 4687

b) 1823

c) 5687

d) 5000

Solution: (a) 4687

Explanation:
Here, every term is multiplied by 5, and adding 2 to get the next term of the series.
1 × 5 + 2 = 7
7 × 5 + 2 = 37
37 × 5 + 2 = 187
187 × 5 + 2 = 937
937 × 5 + 2 = 4687
Hence, 4867 will be our answer.

Question 20: Find the number which would come in place of question mark.

Series: 1, 5, 19, 81, ?

a) 405

b) 411

c) 400

d) 395

Solution: (b) 411

Explanation:
Below is the pattern to crack this series
1 × 2 + 3 = 5
5 × 3 + 4 = 19
19 × 4 + 5 = 81
81 × 5 + 6 = 411
Hence, 411 will be our answer.