Question 1

Complete the series: 2, 5, 10, 17, 26, ?

Accepted Answer

This series follows the pattern where differences between consecutive terms increase by 2 each time. Differences: 3, 5, 7, 9, and the next difference should be 11. So 26 + 11 = 37.

Question 2

Find the missing term in the series:
3, 6, 12, 24, 48, ?
A) 86
B) 96
C) 72
D) 84

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. The missing term is 96.

Question 3

Find the missing term in 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 4

What comes next in the series: 5, 10, 20, 40, 80, ?

Accepted Answer

Each term is multiplied by 2 to obtain the next term. This is a simple geometric progression with common ratio 2.

Question 5

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

Accepted Answer

This series consists of perfect squares: 1², 2², 3², 4², 5², 6². The missing term is 6² = 36.

Question 6

Complete the series: 7, 14, 21, 28, 35, ?

Accepted Answer

This is an arithmetic series where each term increases by 7. The common difference is 7 throughout. So 35 + 7 = 42.

Question 7

Find the missing number: 2, 5, 10, 17, 26, ?, 50

What comes in place of the question mark?

Accepted Answer

This series follows a two-level pattern. The differences are: 5-2=3, 10-5=5, 17-10=7, 26-17=9. The differences themselves increase by 2 each time (3, 5, 7, 9, 11...). So the next difference is 11, and 26+11=37.

Question 8

Look at this series: 3, 6, 12, 24, 48, ?, 192

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. 3 × 2 = 6, 6 × 2 = 12, 12 × 2 = 24, 24 × 2 = 48, 48 × 2 = 96, 96 × 2 = 192.

Question 9

Study the series: 1, 4, 9, 16, 25, ?, 49

Which number should replace the question mark?

Accepted Answer

This series consists of perfect squares: 1², 2², 3², 4², 5², 6², 7². The missing term is 6² = 36.

Question 10

Find the missing term: 7, 14, 28, 56, ?, 224

What should replace the question mark?

Accepted Answer

This is a geometric series where each term is multiplied by 2. 7×2=14, 14×2=28, 28×2=56, 56×2=112, 112×2=224.

Question 11

Study the following number series and find the missing term:

3, 8, 15, 24, 35, ?, 63

What should replace the question mark?

Accepted Answer

This is a two-level pattern (difference-of-differences). First differences: 5, 7, 9, 11, 13, ?. Second differences: 2, 2, 2, 2, 2 (constant). So the next first difference is 15, making the missing term 35 + 15 = 50.

Question 12

Study the series: 5, 11, 23, 47, 95, ?, 383
Find the missing term.

Accepted Answer

Each term is obtained by doubling the previous term and adding 1: 5×2+1=11, 11×2+1=23, 23×2+1=47, 47×2+1=95, 95×2+1=191, 191×2+1=383. The missing term is 191.

Question 13

Study the series: 2, 3, 5, 8, 12, 17, 23, ?, 38
Find the missing term.

Accepted Answer

This is a two-level difference pattern. First differences: 1, 2, 3, 4, 5, 6, 7, ?, 15. Second differences are all 1. The first differences increase by 1 each time, so the missing first difference is 8. Therefore: 23 + 8 = 31.

Question 14

Study the series: 1, 4, 9, 16, 25, ?, 49, 64, 81
Find the missing term.

Accepted Answer

This series consists of perfect squares: 1², 2², 3², 4², 5², ?, 7², 8², 9². The missing term is 6² = 36.

Question 15

Study the series: 3, 7, 15, 31, 63, ?, 255
Find the missing term.

Accepted Answer

Each term follows the pattern: 2ⁿ − 1. The series is 2¹−1=1 (no, starts at 3), actually 2²−1=3, 2³−1=7, 2⁴−1=15, 2⁵−1=31, 2⁶−1=63, 2⁷−1=127, 2⁸−1=255. The missing term is 127.

Question 16

Study the series: 2, 6, 12, 20, 30, 42, ?, 72
Find the missing term.

Accepted Answer

This series follows the pattern n(n+1) where n = 1, 2, 3, 4, 5, 6, 7, 8. So: 1×2=2, 2×3=6, 3×4=12, 4×5=20, 5×6=30, 6×7=42, 7×8=56, 8×9=72. The missing term is 56.

IBPS RRB PO Series Completion

Series Completion— Rules & Concept

Key Points to Remember

Exam-Specific Tips

Series Completion — Practice Questions

60-Second Revision — Series Completion