Series Completion

Explanation / Important formulas:

Series completion section deals with questions in which series of numbers are given, which are generally called as terms of the series. These terms follow a certain pattern throughout.
The candidate is required to recognize this pattern and either complete the given series with the most suitable alternative or find wrong in the series.

  • Number series tests present numerical sequences that follow a logical rule which is based on elementary arithmetic.
  • The difficulty level of these questions can increase in two ways; first, the logic behind the sequence becomes less trivial and demands attention and creativity; second, the missing number can be positioned at an early stage, thus preventing you from deciphering the hidden rule by looking only at the previous numbers in the sequence.

Instructions to take Aptitude Test

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  • Click on the option (A, B, C or D) to figure out the right answer.
  • You can answer multiple times till you get the right answer.
  • Once you get the right answer, explanations (if any) for the same will be showcased down.
  • On click of list, you get to see total no of questions, no of questions you answered and no of questions pending to answer.
  • On click of question number you will go to that particular question.
  • On click of END your test will end.
  • On click of ‘Get Results’ you will get to see correct answer for each questions.

Series Completion - Test



Series Completion - Question and Answers

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Question 1
120, 99, 80, 63, 48, ?
A
35
B
38
C
39
D
40
Question 1 Explanation: 
The pattern is - 21, - 19, - 17, - 15,.....
So, missing term = 48 - 13 = 35.
Question 2
589654237, 89654237, 8965423, 965423, ?
A
58965
B
65423
C
89654
D
96542
Question 2 Explanation: 
The digits are removed one by one from the beginning and the end in order alternately. So as to obtain the subsequent terms of the series.
Question 3
3, 10, 101,?
A
10101
B
10201
C
10202
D
11012
Question 3 Explanation: 
Each term in the series is obtained by adding 1 to the square of the preceding term.
So, missing term = 1012 + 1 = 10202.
Question 4
In the series 2, 6, 18, 54, ...... what will be the 8th term ?
A
4370
B
4374
C
7443
D
7434
Question 4 Explanation: 
Clearly, 2 x 3 = 6, 6 x 3 = 18, 18 x 3 = 54,....
.
So, the series is a G.P. in which a = 2, r = 3.
Therefore 8th term = ar8-1 = ar7 = 2 x 37 = (2 x 2187) = 4374.
Question 5
125,80,45,20,?
A
5
B
8
C
10
D
12
Question 5 Explanation: 
The pattern is - 45, - 35, - 25, .....
So, missing term = 20 - 15 = 5.
Question 6
1, 2, 3, 6, 9, 18, ?, 54
A
18
B
27
C
36
D
81
Question 6 Explanation: 
The pattern is x 2, x 3/2, x 2, x 3/2, x 2,.....
So, missing term = 18 x 3/2 = 27.
Question 7
6, 13, 25, 51, 101, ?
A
201
B
202
C
203
D
205
Question 7 Explanation: 
The pattern is x 2 + 1, x 2 - 1, x 2 + 1, x 2 - 1,.....
So, missing term = 101 x 2 + 1 = 203.
Question 8
5,6,9, 15, ?, 40
A
21
B
25
C
27
D
33
Question 8 Explanation: 
The pattern is + 1, + 3, + 6,....., i.e. + 1, + (1, + 2), + (1 + 2 + 3),.....
So, missing term = 15 + (1 + 2 + 3 + 4) = 25.
Question 9
1, 3, 4, 8, 15, 27, ?
A
37
B
44
C
50
D
55
Question 9 Explanation: 
The sum of any three consecutive terms of the series gives the next term.
So, missing number = 8 + 15 + 27 = 50.
Question 10
3, 4, 7, 7, 13, 13, 21, 22, 31, 34, ?
A
42
B
43
C
52
D
53
Question 10 Explanation: 
The given sequence is a combination of two series :
I. 3, 7, 13, 21, 31, ? and II. 4, 7, 13, 22, 34
The pattern in I is + 4, + 6, + 8, + 10,.....
The pattern in II is + 3, + 6, + 9, + 12,.....
So, missing term = 31 + 12 = 43.
Question 11
198, 194, 185, 169, ?
A
92
B
112
C
136
D
144
Question 11 Explanation: 
The pattern is - 4, - 9, - 16,.....i.e. - 22, - 32, - 42,.....
So, missing pattern = 169 - 52 = 169 - 25 = 144.
Question 12
6, 12, 21, ?, 48
A
33
B
38
C
40
D
45
Question 12 Explanation: 
The pattern is + 6, + 9, + 12, + 15, .....
So, missing term = 21 + 12 = 33.
Question 13
Which term of the series 5, 10, 20, 40, ..... is 1280?
A
10th
B
9th
C
8th
D
None of these
Question 13 Explanation: 
Clearly, 5 x 2 = 10, 10 x 2 = 20, 20 x 2 = 40,.....

So, the series is a G.P. in which a = 5 and r = 2.
Let 1280 be the rath term of the series.
Then, 5x2n-1 = 1280 2n-1 = 256 = 28 n - 1 = 8 n = 9.
Question 14
2, 5, 9, ?, 20, 27
A
14
B
16
C
18
D
24
Question 14 Explanation: 
The pattern is + 3, + 4, + 5, + 6,.....
So, missing term = 9 + 5 = 14.
Question 15
2, 3, 3, 5, 10, 13, ?, 43, 172, 177
A
23
B
38
C
39
D
40
Question 15 Explanation: 
The pattern is + 1, x 1, + 2, x 2, + 3, x 3, + 4, x 4, + 5.
So, missing term = 13 x 3 = 39.
Question 16
9, 27, 31, 155, 161, 1127, ?
A
316
B
1135
C
1288
D
2254
Question 16 Explanation: 
The pattern is x 3, + 4, x 5, + 6, x 7,.....
So, missing term = 1127 + 8 = 1135.
Question 17
2, 1, 2, 4, 4, 5, 6, 7, 8, 8, 10, 11, ?
A
9
B
10
C
11
D
12
Question 17 Explanation: 
The given sequence is a combination of three series :
I. 1st, 4th, 7th, 10th, 13th terms i.e. 2, 4, 6, 8, ?
II. 2nd, 5th, 8th, 11th terms i.e. 1, 4, 7, 10
III. 3rd, 6th, 9th, 12th terms i.e. 2, 5, 8, 11
Clearly, I consists of consecutive even numbers. So, the missing term is 10.
Question 18
Which of the following will not be a number of the series 1, 8, 27, 64, 125,.....?
A
256
B
512
C
729
D
1000
Question 18 Explanation: 
The given series consists of cubes of natural numbers only. 256 is not the cube of
any natural number.
Question 19
13, 32, 24, 43, 35, ?, 46, 65, 57, 76
A
45
B
52
C
54
D
55
Question 19 Explanation: 
The given sequence is a combination of two series:
I. 13, 24, 35, 46, 57 and II. 32, 43, ?, 65, 76
The pattern in both I and II is + 11. So, missing term = 43 + 11 = 54.
Question 20
3, 15, ?, 63, 99, 143
A
27
B
35
C
45
D
56
Question 20 Explanation: 
The terms of the given series are (22 - 1), (42 - 1),....., (82 - 1), (102 - 1), (122 - 1).
So, missing term = (62 - 1) - (36 - 1) = 35.
Question 21
90, 180, 12, 50, 100, 200, ?, 3, 50, 4, 25, 2, 6, 30, 3
A
150
B
175
C
225
D
250
Question 21 Explanation: 
Clearly, 90 = 30 x 3, 180 = 6 x 30, 12 = 2 x 6, 50 = 25 x 2, 100 = 4 x 25, 200 = 50 x 4.
So, missing term = 3 x 50 = 150.
Question 22
48, 24, 96, 48, 192, ?
A
76
B
90
C
96
D
98
Question 22 Explanation: 
The pattern is ÷ 2, x 4, ÷ 2, x 4, .....
So, missing term = 192 ÷ 2 = 96.
Question 23
2,15,41,80,?
A
111
B
120
C
121
D
132
Question 23 Explanation: 
The pattern is + 13, + 26, + 39,.....
So, missing term = 80 + 52 = 132.
Question 24
6, 11, 21, 36, 56, ?
A
42
B
51
C
81
D
91
Question 24 Explanation: 
The pattern is + 5, + 10, + 15, + 20, ...
So, missing term = 56 + 25 = 81.
Question 25
563, 647, 479, 815, ?
A
672
B
386
C
279
D
143
Question 25 Explanation: 
The pattern is + 84, - 168, + 336,.....i.e. + 84, - (84 x 2), + (84 x 22), .....
So, missing term = 815 - (84 x 23) = 815 - 672 = 143.
Question 26
13, 35, 57, 79, 911, ?
A
1110
B
1112
C
1113
D
1315
Question 26 Explanation: 
The terms of the given series are numbers formed by joining together consecutive
odd numbers in order i.e. 1 and 3, 3 and 5, 5 and 7, 7 and 9, 9 and 11, .....
So, missing term = number formed by joining 11 and 13 = 1113.
Question 27
1, 4, 10, 22, 46, ?
A
64
B
86
C
94
D
122
Question 27 Explanation: 
The pattern is + 3, + 6, + 12, + 24,.....
So, missing term = 46 + 48 = 94.
Question 28
66, 36, 18, ?
A
3
B
6
C
8
D
9
Question 28 Explanation: 
Each term in the series is the product of the digits of the preceding term.
So, missing term = 1 x 8 = 8.
Question 29
In the series 3, 9, 15, ...... what will be the 21st term?.
A
117
B
121
C
123
D
129
Question 29 Explanation: 
Clearly, 3 + 6 = 9, 9 + 6 = 15,.....
So, the series is an A.P. in which a = 3 and d = 6.
Therefore 21st term = a + (21 - 1) d = a + 20d = 3 + 20 x 6 = 123.
Question 30
28, 33, 31, 36, ?, 39
A
32
B
34
C
38
D
40
Question 30 Explanation: 
The pattern is + 5, - 2, + 5, - 2,.....
So, missing term = 36 - 2 = 34.
Question 31
1, 9, 25, 49, ?, 121
A
64
B
81
C
91
D
100
Question 31 Explanation: 
The given series consists of squares of consecutive odd numbers
i.e. 12, 32, 52, 72,.....
So, missing term = 92 = 81.
Question 32
2,2,5, 13,28,?
A
49
B
50
C
51
D
52
Question 32 Explanation: 
The pattern is + 0, + 3, + 8, + 15, ..... i.e. + (l2 - 1), + (22 - 1), + (32 - 1), + (42 - 1), .....
So, missing term = 28 + (52 - 1) = 28 + 24 = 52.
Question 33
0, 2, 8, 14, ?, 34
A
20
B
23
C
24
D
25
Question 33 Explanation: 
The pattern is + 2, + 6, + 6, + 10, + 10,.....
So, missing term = 14 + 10 = 24.
Question 34
In the series 10, 17, 24, 31, 38,.....which of the following will be a number of the series ?
A
48
B
346
C
574
D
1003
Question 34 Explanation: 
The given series consists of numbers each of which, on dividing by 7, leaves a
remainder 3. No other number except 346 satisfies the property.
Question 35
240, ?, 120, 40, 10, 2
A
180
B
240
C
420
D
480
Question 35 Explanation: 
The pattern is ÷ 1, ÷ 2, ÷ 3, ÷ 4, ÷ 5.
So, missing term = 240 ÷ 1 = 240
Question 36
2,3,8,27, 112,?
A
226
B
339
C
452
D
565
Question 36 Explanation: 
The pattern is x 1 + 1, x 2 + 2, x 3 + 3, x 4 + 4,.....
So, missing term = 112 x 5 + 5 = 565.
Question 37
6, 17, 39, 72, ?
A
83
B
94
C
116
D
127
Question 37 Explanation: 
The pattern is + 11, + 22, + 33, .....
So, missing term = 72 + 44 = 116.
Question 38
20, 20, 19, 16, 17, 13, 14, 11, ?, ?
A
10, 10
B
10, 11
C
13, 14
D
13, 16
Question 38 Explanation: 
Let the missing terms of the series be x1 and x2.
Thus, the sequence 20, 20, 19, 16, 17, 13, 14, 11, xv x2 is a combination of two series :
I. 20, 19, 17, 14, x1 and II. 20, 16, 13, 11, x2
The pattern in I is - 1, - 2, - 3,......So, missing term, x1 = 14 - 4 = 10.
The pattern in II is - 4, - 3, - 2,......So, missing term, x2 = 11 - 1 = 10.
Question 39
10, 100, 200, 310, ?
A
400
B
410
C
420
D
430
Question 39 Explanation: 
The pattern is + 90 + 100, + 110,.....
So, missing term = 310 + 120 = 430.
Question 40
11, 10, ?, 100, 1001, 1000, 10001
A
101
B
110
C
111
D
None of these
Question 40 Explanation: 
The pattern is - 1, x 10 + 1, - 1, x 10 + 1, - 1, x 10 + 1, .....
So, missing term = 10 x 10 + 1 = 101.
Question 41
2, 7, 27, 107, 427, ?
A
1262
B
1707
C
4027
D
4207
Question 41 Explanation: 
The pattern is + 5, + 20, + 80, + 320, ...... i.e. + (5 x 12), + (5 x 22), + (5 x 42), + (5 x 82),.....
So, missing term = 427 + (5 x 162) = 427 + 1280 = 1707.
Question 42
Complete the series 2,2,5, 13,28,...
A
50
B
51
C
52
D
53
Question 42 Explanation: 
+1^2-1, +2^2-1, +3^2-1,+4^2-1
5^2-1 = 28 + 24
= 52
Question 43
Which number would replace the question mark in series
7,12,19,?,39
A
24
B
28
C
31
D
33
Question 43 Explanation: 
Pattern is , +5, +7, +9
Missing Number = 19+9 = 28
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