Question 1

Find the missing number: 1, 4, 9, 16, 25, ?, 49

Accepted Answer

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

Question 2

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

Accepted Answer

This series follows the pattern where the difference increases by 1 each time. Differences are: +1, +2, +3, +4, +5. So 12 + 5 = 17.

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

Complete the series: 5, 10, 20, 40, 80, ?

Accepted Answer

This is a geometric series where each term is multiplied by 2. The pattern is: 5×2=10, 10×2=20, 20×2=40, 40×2=80, 80×2=160.

Question 5

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

Accepted Answer

This is a series where each term follows the pattern n(n+1), where n = 1, 2, 3, 4, 5, 6, 7. For n=6: 6×7 = 42.

Question 6

What comes next in the series: 3, 7, 15, 31, 63, ?

Accepted Answer

Each term follows the pattern 2^n - 1, where n = 2, 3, 4, 5, 6, 7. For n=7: 2^7 - 1 = 128 - 1 = 127.

Question 7

Find the missing number: 5, 7, 11, 19, 35, ?, 131

Accepted Answer

This series follows the pattern where each term is derived from the previous term using the rule: next = (previous × 2) - 1. Verification: 5×2-1=9 (no, let me recalculate). Actually, the pattern is: each term = (previous × 2) - 3. Check: 5×2-3=7 ✓, 7×2-3=11 ✓, 11×2-3=19 ✓, 19×2-3=35 ✓, 35×2-3=67 ✓, 67×2-3=131 ✓. The missing term is 67.

Question 8

Identify the missing term: 4, 9, 25, 49, 121, 169, ?

Accepted Answer

This series consists of squares of prime numbers: 2²=4, 3²=9, 5²=25, 7²=49, 11²=121, 13²=169. The next prime number is 17, so 17²=289. The missing term is 289.

Question 9

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 (constant). So the next first difference is 15, making the missing term 35 + 15 = 50.

Question 10

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

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. The missing term is 96.

Question 11

Complete the series: 2, 5, 10, 17, 26, 37, ?

Accepted Answer

This series follows a second-order difference pattern. The differences between consecutive terms are: 3, 5, 7, 9, 11, and the next difference should be 13. So 37 + 13 = 50. The differences themselves increase by 2 each time (3, 5, 7, 9, 11, 13).

Question 12

What comes next? 1, 1, 2, 3, 5, 8, 13, 21, ?

Accepted Answer

This is the Fibonacci sequence where each term is the sum of the two preceding terms. 1+1=2, 1+2=3, 2+3=5, 3+5=8, 5+8=13, 8+13=21, 13+21=34. The missing term is 34.

Question 13

Analyze the series: 1, 4, 10, 20, 35, 56, ?, 120
What is the missing number?

Accepted Answer

This series follows the pattern of triangular numbers multiplied by position, or equivalently, the differences form a sequence: 3, 6, 10, 15, 21, 28, 36. These are triangular numbers. The missing term is 56 + 28 = 84.

Question 14

Determine the missing term: 5, 6, 8, 11, 15, 20, 26, ?, 41
What replaces the question mark?

Accepted Answer

First differences: 1, 2, 3, 4, 5, 6, 7, ?, 15. The differences increase by 1 each time. The missing first difference is 8, so the missing term is 26 + 8 = 34.

Question 15

Find the missing term in the series: 2, 6, 13, 23, 36, 52, 71, ?, 117
What is the missing number?

Accepted Answer

First differences: 4, 7, 10, 13, 16, 19, 22, ?, 46. Second differences are constant at 3. The missing first difference is 25, so the missing term is 71 + 25 = 96.

Question 16

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

Accepted Answer

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

Question 17

Complete the series: 3, 7, 14, 24, 37, 53, ?, 98
Find the missing term.

Accepted Answer

First differences: 4, 7, 10, 13, 16, 19, 22, 25. These form an arithmetic sequence with common difference 3. The missing first difference is 22, so the missing term is 53 + 22 = 75.

SBI PO Series Completion

Series Completion— Rules & Concept

Key Points to Remember

Exam-Specific Tips

Series Completion — Practice Questions

60-Second Revision — Series Completion