Series Completion Reasoning is a type of Verbal Reasoning question that requires you to identify the pattern in a sequence of numbers, letters, or symbols and complete the series by filling in the missing terms.
With practice, you can learn to solve series completion questions quickly and accurately. This will help you improve your performance on standardized tests and job interviews.
Series Completion Concept :
To solve Series completion questions you need to follow the given below steps -
Step 1. Identify the Pattern:
- Arithmetic Sequence: Each term increases or decreases by a constant difference.
- Geometric Sequence: Each term is a multiple of the previous term by a constant ratio.
- Mixed Operations: Some series combine multiple operations (addition, multiplication, etc.) in a repetitive pattern.
- Identify each step’s operation (e.g., add, multiply, subtract) and apply accordingly.
- Squares and Cubes: Series may follow a pattern based on squares (e.g., 1, 4, 9, 16...) or cubes (e.g., 1, 8, 27, 64...).
- Fibonacci Series: Each term is the sum of the two preceding terms.
- Prime Number Series: Series may consist of prime numbers in ascending order. Identify the primes and look for any additional pattern or constant.
- Alternate Series: Series with two or more distinct patterns alternating. Identify each sequence individually (e.g., one increases, another decreases).
- Difference or Ratio Between Terms: Look at differences or ratios between terms to uncover hidden patterns.
- Reverse or Palindromic Series: Sometimes numbers repeat in reverse order or mirror around a central point.
Step 2. Use Formulas:
Once the pattern is identified, apply relevant formulas if required to find the missing term or complete the series.
Step 3. Test and Verify:
Verify the discovered pattern fits all terms before completing the series.
Each pointer guides a step in identifying the underlying rule or operation, helping to complete the series accurately.
Series Completion Questions with Answers
1. In the series 2, 5, 10, 17, 26, ? ...... what will be the next term?
a) 38
b) 40
c) 37
d) 44
Answer: c) 42
Explanation: The differences between consecutive numbers are increasing by 2:
(5 - 2) = 3, (10 - 5) = 5, (17 - 10) = 7, (26 - 17) = 9.
The next difference should be 11, so 26 + 11 = 37.
2. What comes next in the series: 2P, 5M, 10J, 17G, ...?
a) 24 F
b) 42 P
c) 26 D
d) 12 A
Answer: c) 26 D
Explanation: The differences between consecutive numbers are increasing by 2:
(5 - 2) = 3, (10 - 5) = 5, (17 - 10) = 7, (26 - 17) = 9.
The next difference should be 9, so Number will be 26.
The Alphabet pattern is subtracting 3 positions to the alphabet each time:
P (16th), M (13th), J (10th), G (7th),
The next letter will be G (7th) - 3 = D (4th)
So Answer will be 26 D.
3. What is the missing Alphabet in the series: W, S, O, K, ?
a) C
b) F
c) J
d) None of these
Answer: d) None of these
Explanation: The pattern is moving backward in the alphabet, skipping 4 letters each time:
W (23rd), S (19th), O (15th), K (11th).
The next letter will be G (7th).
4. What comes next in the series: 1, 2, 6, 24, 120, ....?
a) 720
b) 240
c) 150
d) 360
Answer: a) 720
Explanation: The pattern follows the factorials of numbers:
1! = 1, 2! = 2, 3! = 6, 4! = 24, 5! = 120.
The next term is 6! = 720.
5. What is the missing number in the series: 2, 5, 11, _, 47, 95?
a) 17
b) 23
c) 29
d) 47
Answer: b) 23
Explanation: The series follows a pattern where each number is doubled and 1 is added. So, to find the missing number, we double 11 and add 1.
11 * 2 + 1 = 23.
6. What comes next in the series: 10, B, 100, D, 200, G, 310, ...?
a) J 400
b) K 430
c) L 390
d) J 430
Answer: b) K 430
Explanation: The positions of the letters are increasing adding by 2, 3, 4, and 5 alphabet
i.e. B+2 = D, D+3 = G, G+4 = K
And The positions of the numbers are increasing adding by 90, 100, 110, 120, and so on...
i.e. 10+90 = 100, 100+100 = 200, 200+110 = 310, 310+120 = 430
7. What is the missing number in the series: 125, 170, 135, .... , 145, ?
a) 140
b) 160
c) 115
d) None of these
Answer: b) 160
Explanation: The series pattern is -
125 + 45 = 170 , 170 - 35 = 135, 135 + 25 = 160, 160 -15 = 145
So, the missing number will be 160
8. What comes next in the series: 144, 121, 100, 81, ...?
a) 64
b) 49
c) 36
d) 25
Answer: a) 64
Explanation: This series represents the squares of consecutive decreasing natural numbers: 12^2 = 144, 11^2 = 121, 10^2 = 100, 9^2 = 81, and so on. Therefore, the next term is 8^2 = 64.
9. What is the missing number in the series: 2, 6, 12, ....., 42?
a) 18
b) 42
c) 24
d) 36
Answer: d) 36
Explanation: The series follows a pattern where alternate numbers are multiplied by 3, and then 6 is added.
So, 2*3 = 6 , 6 + 6 = 12, 12*3 = 36 , 36 + 6 = 42
10. What comes next in the series: 3, 6, 18, 72, ...?
a) 216
b) 360
c) 432
d) 648
Answer: b) 360
Explanation: This series represents a pattern where numbers are multiplied by 2, 3, 4, 5 and so on....
So the next term will be - 72*5 = 360
Read More :