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Question

In the following question, which set of letters and numbers, when sequentially placed at the gaps in the given series, shall complete it?

1_2x_bb_yy_cc_6zzz

This question was previously asked in
RRB ALP 2018 CBT 2 Fitter Question Paper (21-Jan-2019) (Shift 3)
The correct answer is

a345c

Understanding the Series Completion Question

This question asks us to identify the pattern in a given series of letters and numbers and find the set of characters that correctly fills the gaps to complete the sequence. The series is presented as:

1_2x_bb_yy_cc_6zzz

There are five gaps in the series, indicated by underscores.

Analyzing the Options for the Series Gaps

We are provided with four options, each containing five characters to fill the five gaps:

  1. a345c
  2. 3a45b
  3. 3a4b5
  4. 3a45c

We need to test each option by placing its characters sequentially into the gaps to see which one reveals a consistent pattern in the complete series.

Step-by-Step Solution: Identifying the Pattern

Let's take the first option, a345c, and insert its characters into the gaps in the series:

Original series: 1_2x_bb_yy_cc_6zzz

Inserting a345c: 1a2x3bb4yy5ccc6zzz

The complete series becomes: 1a2x3bb4yy5ccc6zzz

Breaking Down the Series into Segments

Let's look at how the original parts and the inserted characters combine. The original series structure suggests segments separated by the gaps. When filled with a345c, we can observe segments by pairing each original part (except the last one) with the character immediately following it in the combined sequence:

  • First original part 1 + first inserted character a = 1a
  • Second original part 2x + second inserted character 3 = 2x3
  • Third original part bb + third inserted character 4 = bb4
  • Fourth original part yy + fourth inserted character 5 = yy5
  • Fifth original part cc + fifth inserted character c = ccc
  • The last original part is 6zzz.

So, the series can be viewed as a sequence of these segments: 1a, 2x3, bb4, yy5, ccc, 6zzz.

Identifying the Number Sequence Pattern

Let's look at the numbers present across these segments:

  • In 1a, we have the number \(1\).
  • In 2x3, we have the numbers \(2\) and \(3\).
  • In bb4, we have the number \(4\).
  • In yy5, we have the number \(5\).
  • In ccc, there is no number.
  • In 6zzz, we have the number \(6\).

Arranging the numbers in the order they appear in the series, we get \(1, 2, 3, 4, 5, 6\). This is a clear sequence of consecutive integers. This strong pattern supports Option 1.

Identifying the Letter Repetition Pattern

Now let's look at the letter parts of the segments:

  • 1a contains letter a. Repetition count: \(1\).
  • 2x3 contains letter x. Repetition count: \(1\).
  • bb4 contains letter bb. Repetition count: \(2\).
  • yy5 contains letter yy. Repetition count: \(2\).
  • ccc contains letter ccc. Repetition count: \(3\). (This is formed by the original cc and the inserted c).
  • 6zzz contains letter zzz. Repetition count: \(3\).

The sequence of letter repetition counts is \(1, 1, 2, 2, 3, 3\). This is another consistent pattern where repetition counts \(1\), \(2\), and \(3\) each appear twice.

Confirming the Pattern with Option 1

Option 1 (a345c) successfully creates a series where:

  • Numbers \(1\) through \(6\) appear sequentially.
  • Letters appear in groups with repetition counts \(1, 1, 2, 2, 3, 3\).

Let's quickly check other options. If we used Option 2 (3a45b), the numbers would be inserted as 3, a, 4, 5, b. The series would be 132xabb4yy5ccb6zzz. The number sequence would be 1, 3, 2, 4, 5, 6, which is not sequential. Similarly, other options will also fail to produce the clear sequential number pattern \(1, 2, 3, 4, 5, 6\).

Thus, Option 1 is the only set of characters that fits the identified patterns.

Revision Table: Series Pattern Analysis

Segment Numbers Present Letter Group Letter Repetition Count
1a \(1\) a \(1\)
2x3 \(2, 3\) x \(1\)
bb4 \(4\) bb \(2\)
yy5 \(5\) yy \(2\)
ccc None ccc \(3\)
6zzz \(6\) zzz \(3\)

The table shows the number sequence \(1, 2, 3, 4, 5, 6\) appearing across the segments and the letter repetition counts \(1, 1, 2, 2, 3, 3\).

Additional Information on Series Patterns

Series completion questions often involve various types of patterns. Recognizing these patterns is key to solving such problems. Some common patterns include:

  • Arithmetic Progressions: Numbers increasing or decreasing by a constant difference.
  • Geometric Progressions: Numbers increasing or decreasing by a constant ratio.
  • Fibonacci Series: Each number is the sum of the two preceding ones.
  • Alphabetical Patterns: Letters following sequence (A, B, C...), skipping letters (A, C, E...), or moving positions.
  • Combined Patterns: Involvement of both numbers and letters, sometimes with alternating patterns or patterns based on the position or type of character.
  • Repetition Patterns: Characters or groups of characters repeating in a predictable way.
  • Positional Patterns: The position of elements within the series determines the pattern.

Analyzing the given elements carefully and testing potential rules based on number sequences, alphabetical order, repetitions, or positions is a good strategy for solving series completion questions.

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