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Question

In the following question, select the missing number from the given series.

23, 11, 34, 45, 79, ?

This question was previously asked in
SSC Stenographer 2017 Previous Year Paper (14-Sep-2017) (Shift 1)
The correct answer is

124

Understanding Number Series Patterns

Let's analyze the given number series: 23, 11, 34, 45, 79, ?. We need to find the missing number that follows the pattern established by the preceding terms in the series.

Number series questions often involve identifying a relationship between consecutive terms. Let's examine the relationship between the numbers in this specific series.

Consider the first few terms:

  • The first term is 23.
  • The second term is 11.

Let's see if the third term is related to the first two.

  • First term + Second term = 23 + 11 = 34.

The third term is indeed 34. This suggests a pattern where each term is the sum of the two terms before it. This is similar to the famous Fibonacci sequence pattern.

Let's check if this pattern holds true for the subsequent terms:

  • Second term + Third term = 11 + 34 = 45. (This matches the fourth term).
  • Third term + Fourth term = 34 + 45 = 79. (This matches the fifth term).

The pattern holds consistently. The pattern is that the current term is the sum of the previous two terms.

Calculating the Missing Number in the Series

Following the identified pattern, the missing number (which is the sixth term in the series) should be the sum of the fourth term and the fifth term.

  • Fourth term = 45
  • Fifth term = 79

Missing Number = Fourth term + Fifth term

Missing Number = 45 + 79

Let's perform the addition:

\( 45 + 79 = 124 \)

So, the missing number in the series is 124.

Verification of the Number Series Pattern

Let's write down the series including the calculated missing number to see the complete pattern:

23, 11, 34, 45, 79, 124

Term Number Value Calculation (if applicable)
1st 23 -
2nd 11 -
3rd 34 23 + 11
4th 45 11 + 34
5th 79 34 + 45
6th (Missing) 124 45 + 79

The series clearly follows the pattern where each term is the sum of the two preceding terms. Therefore, the missing number is 124.

Revision Table: Key Concepts in Number Series

Concept Description Example Pattern Type
Arithmetic Series Constant difference between consecutive terms. 2, 5, 8, 11, ... (Difference is 3)
Geometric Series Constant ratio between consecutive terms. 3, 6, 12, 24, ... (Ratio is 2)
Fibonacci-like Series Each term is the sum of the previous two terms (or a variation). 1, 1, 2, 3, 5, 8, ... or the series in this question.
Difference Series The difference between consecutive terms follows a pattern. 2, 3, 5, 8, 12, ... (Differences are 1, 2, 3, 4)
Mixed Series Combination of two or more patterns or alternating patterns. Sometimes involve squares, cubes, or other mathematical operations.

Additional Information on Identifying Number Series Patterns

Solving number series questions requires careful observation and trying different approaches. Here are some tips:

  • Look at the difference between consecutive terms. Is it constant, increasing, decreasing, or following another pattern?
  • Look at the ratio between consecutive terms. Is it constant?
  • Consider if terms are related to their position number (e.g., \(n^2\), \(n^2+1\)).
  • Check if terms are sums or differences of previous terms, like in the Fibonacci pattern seen in this series.
  • Look for alternating patterns (e.g., pattern for 1st, 3rd, 5th terms and a different pattern for 2nd, 4th, 6th terms).
  • Think about squares, cubes, prime numbers, or other special number sequences.

Practicing different types of number series problems helps in quickly identifying the underlying pattern.

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