Question 1

What is the next term in the series: 2, 3, 5, 8, 12, 17, ?

Accepted Answer

This series has differences that increase by 1 each time. The differences are: 3-2=1, 5-3=2, 8-5=3, 12-8=4, 17-12=5. The next difference should be 6, so the missing term is 17+6=23.

Question 2

Find the missing number: 1, 4, 9, 16, 25, 36, ?

Accepted Answer

This series consists of perfect squares: 1²=1, 2²=4, 3²=9, 4²=16, 5²=25, 6²=36, 7²=49. The missing term is 49.

Question 3

What comes next in the series: 5, 7, 11, 13, 17, 19, ?

Accepted Answer

This series consists of pairs of consecutive prime numbers. The pairs are (5,7), (11,13), (17,19). The next pair of consecutive primes after 19 is (23,29), but the pattern shows we take the first prime of each pair: 5, 11, 17, then the second: 7, 13, 19. Following the alternating pattern, the next term is 23 (the next prime after 19).

Question 4

Find the missing term in the series: 2, 5, 10, 17, 26, ?

Accepted Answer

This is a simple arithmetic series with increasing differences. The differences between consecutive terms are: 5-2=3, 10-5=5, 17-10=7, 26-17=9. The differences form an arithmetic sequence (3, 5, 7, 9, ...). The next difference should be 11, so the missing term is 26+11=37.

Question 5

Find the missing term in the series:
2, 5, 10, 17, 26, ?

(a) 35
(b) 36
(c) 37
(d) 38

Accepted Answer

The series follows the pattern where each term is obtained by adding consecutive odd numbers to the previous term.

2 + 3 = 5
5 + 5 = 10
10 + 7 = 17
17 + 9 = 26
26 + 11 = 37

The differences form an arithmetic sequence: 3, 5, 7, 9, 11 (odd numbers increasing by 2).

Therefore, the missing term is 37.

Question 6

Complete the series: 3, 6, 12, 24, 48, ?

Accepted Answer

This is a geometric series where each term is multiplied by 2 to get the next term. 3×2=6, 6×2=12, 12×2=24, 24×2=48, 48×2=96.

Question 7

Find the missing term in the series: 2, 6, 12, 20, 30, ?, 56

Accepted Answer

This is a second-order difference series. First differences: 4, 6, 8, 10, 12, ?. Second differences are constant at 2. So the next first difference is 14, making the missing term 30 + 14 = 44.

Question 8

Find the missing term in the following series:
3, 6, 12, 24, 48, ?, 192

Accepted Answer

This is a geometric progression where each term is obtained by multiplying the previous term by 2.

Step 1: Identify the pattern
- 3 × 2 = 6
- 6 × 2 = 12
- 12 × 2 = 24
- 24 × 2 = 48
- 48 × 2 = 96 (missing term)
- 96 × 2 = 192

Step 2: Verify the pattern
Each number is double the previous number. The missing term should be 96.

Step 3: Check with the last given term
96 × 2 = 192 ✓ (This matches the final term, confirming our answer)

The answer is 96.

Question 9

Study the following series and find the missing term:

3, 6, 12, 24, ?, 96

What should replace the question mark?

Accepted Answer

This is a geometric series where each term is multiplied by 2 to get the next term. The pattern is: 3 × 2 = 6, 6 × 2 = 12, 12 × 2 = 24, 24 × 2 = 48, 48 × 2 = 96. Therefore, the missing term is 48.

Question 10

Complete the series: 1, 4, 9, 16, 25, 36, ?, 64

Accepted Answer

This is a series of perfect squares: 1², 2², 3², 4², 5², 6², 7², 8². The missing term is 7² = 49.

Question 11

What comes next in the series: 2, 3, 5, 8, 13, 21, ?

Accepted Answer

This is the Fibonacci sequence where each term is the sum of the two preceding terms. 13 + 21 = 34.

Question 12

Find the missing number: 5, 11, 23, 47, 95, ?

Accepted Answer

Each term is obtained by multiplying the previous term by 2 and subtracting 1. Pattern: (n × 2) − 1. So 95 × 2 − 1 = 189.

Question 13

Complete the series: 3, 7, 15, 31, 63, ?

Accepted Answer

Each term is obtained by multiplying the previous term by 2 and adding 1. Pattern: (n × 2) + 1. So 63 × 2 + 1 = 127.

Question 14

What comes next? 2, 6, 12, 20, 30, 42, ?, 72

Accepted Answer

These are products of consecutive integers: 1×2, 2×3, 3×4, 4×5, 5×6, 6×7, 7×8, 8×9. The missing term is 7×8 = 56.

Question 15

Find the missing number: 3, 6, 11, 18, 27, 38, ?, 66

Accepted Answer

First differences: 3, 5, 7, 9, 11, 13, ?. These are consecutive odd numbers. The next difference is 15, so the missing term is 38 + 15 = 53.

Question 16

Complete the series: 1, 4, 10, 20, 35, 56, ?, 120

Accepted Answer

These are triangular numbers multiplied by increasing integers, or equivalently, the differences form the sequence 3, 6, 10, 15, 21, 28... (triangular numbers). The missing term is 56 + 28 = 84.

Question 17

Complete the series: 5, 7, 11, 19, 35, 67, ?, 259

Accepted Answer

Each term is double the previous term minus 3: 7 = 2(5)−3, 11 = 2(7)−3, 19 = 2(11)−3, 35 = 2(19)−3, 67 = 2(35)−3. So the missing term is 2(67)−3 = 131.

Question 18

Study the following series carefully and find the missing term:

2, 3, 7, 16, 32, ?, 130

What should replace the question mark?

Accepted Answer

This is a two-level difference pattern. First differences: 1, 4, 9, 16, ?, ?. These are perfect squares (1², 2², 3², 4², 5², 6²). So the second differences form the sequence 1, 4, 9, 16, 25, 36. The missing term is 32 + 25 = 57.

Question 19

Find the missing term in the series: 2, 3, 5, 8, 12, 17, ?, 34

Accepted Answer

This is a second-order difference series. First differences: 1, 2, 3, 4, 5, 6, ?. Second differences are all 1 (constant). So the next first difference is 7, making the missing term 17 + 7 = 24.

RRB NTPC Series Completion

Series Completion— Rules & Concept

Key Points to Remember

Exam-Specific Tips

Series Completion — Practice Questions

60-Second Revision — Series Completion