# Number Series Aptitude Q & A – Part 7

*This is the Part 7 Aptitude Questions and Answers section on “Number series“ with explanation for various interview, competitive examination and entrance test. Solved examples with detailed answer description, explanation are given and it would be easy to understand. *

**61. 75 65 85 55 45 85 35**

A. 25 15

B. 25 85

C. 35 25

D. 85 35

**Answer: **

B. 25 85

**Explanation:**

This is a simple subtraction series in which a random number, 85, is interpolated as every third number. In the subtraction series, 10 is subtracted from each number to arrive at the next.

**62. 11 16 21 26 31 36 41**

A. 47 52

B. 46 52

C. 45 49

D. 46 51

**Answer:**

D. 46 51

**Explanation:**

In this simple addition series, each number is 5 more than the previous number.

**63. Look at this series: 21, 9, 21, 11, 21, 13, 21, … What number should come next?**

A. 14

B. 15

C. 21

D. 23

**Answer:**

B. 15

**Explanation:**

In this alternating repetition series, the random number 21 is interpolated every other number into an otherwise simple addition series that increases by 2, beginning with the number 9.

**64. Look at this series: 58, 52, 46, 40, 34, … What number should come next?**

A. 26

B. 28

C. 30

D. 32

**Answer:**

B. 28

**Explanation:**

This is a simple subtraction series. Each number is 6 less than the previous number.

**65. 42 40 38 35 33 31 28**

A. 25 22

B. 26 23

C. 26 24

D. 25 23

**Answer:**

C. 26 24

**Explanation:**

This is an alternating subtraction series in which 2 is subtracted twice, then 3 is subtracted once, then 2 is subtracted twice, and so on.

**66. 13 29 15 26 17 23 19**

A. 21 23

B. 20 21

C. 20 17

D. 25 27

**Answer:**

B. 20 21

**Explanation:**

Here, there are two alternating patterns, with every other number following a different pattern. The first pattern begins with 13 and adds 2 to each number to arrive at the next; the alternating pattern begins with 29 and subtracts 3 each time.

**67. Look at this series: 70, 71, 76, __, 81, 86, 70, 91, … What number should fill the blank?**

A. 70

B. 71

C. 80

D. 96

**Answer:**

A. 70

Explanation:

In this series, 5 is added to the previous number; the number 70 is inserted as every third number.

**68. Look at this series: 8, 43, 11, 41, __, 39, 17, … What number should fill in the blank?**

A. 8

B. 14

C. 43

D. 44

**Answer:**

B. 14

**Explanation:**

This is a simple alternating addition and subtraction series. The first series begins with 8 and adds 3; the second begins with 43 and subtracts 2.

**69. 28 25 5 21 18 5 14**

A. 11 5

B. 10 7

C. 11 8

D. 5 10

**Answer:**

A. 11 5

**Explanation:**

This is an alternating subtraction series with the interpolation of a random number, 5, as every third number. In the subtraction series, 3 is subtracted, then 4, then 3, and so on.

**70. 10 20 25 35 40 50 55**

A. 70 65

B. 60 70

C. 60 75

D. 65 70

**Answer:**

D. 65 70

**Explanation:**

This is an alternating addition series, in which 10 is added, then 5, then 10, and so on.

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