Sequence and Series Questions and Solutions : Logical Reasoning

• 1. Which number would replace underline mark in the series?
2, 5, 10, 17, ---, 37
A.) 27
B.) 24
C.) 26
D.) 28

Here the difference between the consecutive terms is increase by 2
5 - 2 = 3,
10 - 5 = 5,
17 - 10 = 7,
then 17 + 9 = 26.

• 2. Which number would replace underline mark in the series?
1, 6, 26,_____, 426.
A.) 86
B.) 76
C.) 106
D.) 96

Here the difference between the consecutive terms is multiplied by 4.
The difference of the two consecutive numbers is 5, 20, .....
5 × 4 = 20
20 × 4 = 80
26 + 80 = 106.

• 3. Which number would replace underline mark in the series?
1, 20, 58, ____, 191.
A.) 105
B.) 115
C.) 111
D.) 116

Here the difference between the two consecutive terms is 19, 38, 57, 76
58 + 57 = 115

• 4. 2, 10, 40, 120,____
A.) 240
B.) 360
C.) 470
D.) 210

Here the series is a multiplication series.
The order of the multiplication is ×5, ×4, ×3, ×2
120 × 2 = 240

• 5. 18 21 25 18 29 33 18
What numbers should come next ?
A.) 43 18
B.) 41 44
C.) 37 41
D.) 38 41

This is a simple addition series with a random number, 18, interpolated as every third number.
In the series, 4 is added to each number except 18, to arrive at the next number

• 6. 20 20 17 17 14 14 11 What numbers should come next ?
A.) 8 8
B.) 8 9
C.) 11 8
D.) 8 9s

This is a simple subtraction with repetition series.
It begins with 20, which is repeated, then 3 is subtracted, resulting in 17, which is repeated, and so on.
Rule = (1st no) (1st no) (1st no - 3 = 2nd no) (2nd no repeat) (2nd no - 3 = 3rd no) (3rd no repeat). . .
Now (20) (20) (20 - 3 = 17) (17) (17 - 3 = 14) (14) (14 - 3 = 11) (11) (11 - 3 = 8) (8)
So the answer is e = 11 8.

• 7. 3 13 18 23 28 33
What number should come next?
A.) 38 43
B.) 37 42
C.) 38 44
D.) 39 44

In this simple addition series, each number is 5 greater than the previous number.
Rule = (1st no) (1st no + 5 = 2nd no) (2nd no + 5 = 3rd no) . . .
Now (3) (3 + 5 = 8) (8 + 5 = 13) (13 + 5 = 18) (18 + 5 = 23) (23 + 5 = 28) (28 + 5 = 33) (33 + 5 = 38) (38 + 5 = 43)
So the answer is c = 38 43

• 8. Look at this series: 1000, 200, 40, . . .
What number should come next?
A.) 10
B.) 8
C.) 9
D.) 12

This is a simple division series.
Each number is divided by 5.
Rule = (1st number / 5 = 2nd number) (2nd number / 5 = 3rd number)....
Now, (1000 / 5 = 200), (200 / 5 = 40), (40 / 5 = 8)...
So answer is a = 8.

• 9. Look at this series: 7, 10, 8, 11, 9, 12, . . .
What number should come next?
A.) 7
B.) 10
C.) 15
D.) 18

This is a simple alternating addition and subtraction series.
In the first pattern, 3 is added;
In the second pattern, 2 is subtracted.
Rule =(1st number) (1st number + 3 = 2nd number) (2nd number - 2 = 3rd number) (3rd number + 3 = 4th number)
Now (7) (7 + 3 = 10) (10 - 2 = 8) (8 + 3 = 11) (11 - 2 = 9) (9 + 3 = 12) (12 - 2 = 10)...
So the answer is b = 10.

• 10. 1, 2, 3, 10, ____, 9802
A.) 199
B.) 999
C.) 99
D.) 298

12 + 1 = 2

22 - 1 = 3

32 + 1 = 10

102 - 1 = 99.

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