Infosys Number Series Questions: Repeated Aptitude Problems

Types of Number Series Patterns

Before solving number series questions, it’s important to recognize the common types of patterns:

1. Arithmetic Series (Addition/Subtraction)

Each number is obtained by adding or subtracting a fixed number.
Example: 2, 5, 8, 11, 14, ? (Add 3)
Answer: 17

2. Geometric Series (Multiplication/Division)

Each term is obtained by multiplying or dividing by a fixed number.
Example: 3, 6, 12, 24, ? (Multiply by 2)
Answer: 48

3. Square/Cube Series

Numbers follow a pattern of squares or cubes.
Example: 1, 4, 9, 16, 25, ? (Squares of 1, 2, 3, …)
Answer: 36

4. Fibonacci Series

Each term is the sum of the previous two terms.
Example: 0, 1, 1, 2, 3, 5, 8, ?
Answer: 13

5. Alternating Series

Different operations are used in alternate steps.
Example: 2, 4, 8, 7, 14, 28, 27, ?
Answer: 54 (Double and subtract 1)

Commonly Asked Number Series Questions in Infosys

Here are some frequently asked questions with answers and explanations.

1. Find the missing number in the series:

2, 5, 10, 17, 26, ?

A) 37
B) 36
C) 38
D) 40

Answer: A) 37

Explanation:

The pattern follows:
2 + 3 = 5,
5 + 5 = 10,
10 + 7 = 17,
17 + 9 = 26,
26 + 11 = 37 (Increasing odd numbers)

So, the missing number is 37.

2. Find the next number in the sequence:

100, 96, 92, 88, ?

A) 80
B) 84
C) 85
D) 82

Answer: B) 84

Explanation:

Each term is obtained by subtracting 4:
100 – 4 = 96,
96 – 4 = 92,
92 – 4 = 88,
88 – 4 = 84

So, the missing number is 84.

3. What comes next in the series?

1, 8, 27, 64, 125, ?

A) 150
B) 216
C) 343
D) 512

Answer: B) 216

Explanation:

The numbers are cubes of natural numbers:
13=11^3 = 113=1, 23=82^3 = 823=8, 33=273^3 = 2733=27, 43=644^3 = 6443=64, 53=1255^3 = 12553=125, 63=2166^3 = 21663=216

So, the missing number is 216.

4. Identify the missing term:

7, 10, 16, 28, ?

A) 34
B) 46
C) 52
D) 56

Answer: B) 46

Explanation:

Pattern:
7 + 3 = 10,
10 + 6 = 16,
16 + 12 = 28,
28 + 18 = 46 (Each step doubles the previous addition)

So, the missing number is 46.

5. Find the next term in the sequence:

2, 3, 5, 7, 11, ?

A) 12
B) 15
C) 13
D) 17

Answer: C) 13

Explanation:

The series consists of prime numbers:
2, 3, 5, 7, 11, 13

So, the missing number is 13.

Tips to Solve Number Series Questions Quickly

1. Look for a Pattern – Identify if the numbers increase or decrease using addition, subtraction, multiplication, or division.
2. Check for Squares/Cubes – If the numbers increase rapidly, check if they are squares or cubes.
3. Find the Difference – If the difference between numbers is consistent, it could be an arithmetic series.
4. Observe Alternate Terms – Sometimes, alternate numbers follow a different pattern.
5. Use the Options – If you’re unsure, try each option in the pattern to see which fits best.
6. Practice Regularly – The more you practice, the quicker you’ll recognize patterns.

Final Thoughts

Number series questions are frequently asked in Infosys placement exams, and practicing different types of patterns will help you solve them faster. Focus on arithmetic progressions, geometric sequences, squares, cubes, Fibonacci numbers, and alternating series to improve your accuracy.