# Number Series Aptitude Q & A – Part 6

*This is the Part 6 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. *

**51. Look at this series: 80, 10, 70, 15, 60, … What number should come next?**

A. 20

B. 25

C. 30

D. 50

**Answer:**

A. 20

**Explanation:**

This is an alternating addition and subtraction series. In the first pattern, 10 is subtracted from each number to arrive at the next. In the second, 5 is added to each number to arrive at the next.

**52. Look at this series: 8, 6, 9, 23, 87 , … What number should come next?**

A. 128

B. 226

C. 324

D. 429

**Answer:**

D. 429

**Explanation:**

8 x 1 – 2 = 6

6 x 2 – 3 = 9

9 x 3 – 4 = 23

23 x 4 – 5 = 87

87 x 5 – 6 = 429 …

**53. Look at this series: 22, 21, 23, 22, 24, 23, … What number should come next?**

A. 22

B. 24

C. 25

D. 26

**Answer:**

C. 25

**Explanation:**

In this simple alternating subtraction and addition series; 1 is subtracted, then 2 is added, and so on.

**54. Look at this series: 53, 53, 40, 40, 27, 27, … What number should come next?**

A. 12

B. 14

C. 27

D. 53

**Answer:**

B. 14

**Explanation:**

In this series, each number is repeated, then 13 is subtracted to arrive at the next number.

**55. 2 3 4 5 6 4 8**

A. 9 10

B. 4 8

C. 10 4

D. 9 4

**Answer:**

D. 9 4

**Explanation:**

This is an alternating addition series with a random number, 4, interpolated as every third number. In the main series, 1 is added, then 2 is added, then 1, then 2, and so on.

**56. 17 17 34 20 20 31 23**

A. 26 23

B. 34 20

C. 23 33

D. 23 28

**Answer:**

D. 23 28

**Explanation:**

This is an alternating subtraction series with repetition. There are two different patterns here. In the first, a number repeats itself; then 3 is added to that number to arrive at the next number, which also repeats. This gives the series 17, 17, 20, 20, 23, and so on. Every third number follows a second pattern, in which 3 is subtracted from each number to arrive at the next: 34, 31, 28.

**57. 34 30 26 22 18 14 10**

A. 8 6

B. 6 4

C. 14 18

D. 6 2

**Answer:**

D. 6 2

**Explanation:**

This is a simple subtraction series, in which 4 is subtracted from each number to arrive at the next.

**58. 32 31 32 29 32 27 32**

A. 25 32

B. 31 32

C. 29 32

D. 25 30

**Answer:**

A. 25 32

**Explanation:**

This is an alternating repetition series. The number 32 alternates with a series in which each number decreases by 2.

**59. Look at this series: 83, 73, 93, 63, __, 93, 43, … What number should fill the blank?**

A. 33

B. 53

C. 73

D. 93

**Answer:**

B. 53

**Explanation:**

This is a simple subtraction series in which a random number, 93, is interpolated as every third number. In the subtraction series, 10 is subtracted from each number to arrive at the next.

**60. Look at this series: XXIV, XX, __, XII, VIII, … What number should fill the blank?**

A. XXII

B. XIII

C. XVI

D. IV

**Answer:**

C. XVI

**Explanation:**

This is a simple subtraction series; each number is 4 less than the previous number.

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