What should come in place of '?' in the given series? 12 20 23 42 45 ?

Appeared in: NCL (Northern Coalfields Limited)-NO

Explanation

The sequence is a combination of two interleaved series based on odd and even positions.
The first series (1st, 3rd, 5th terms) is 12, 23, 45. The difference between consecutive terms doubles: first it's 11 (23-12), then it's 22 (45-23).
The second series (2nd, 4th, 6th terms) is 20, 42, ?. The difference between the first two terms is 22 (42-20).
Following the same doubling logic, the next difference in the second series should be 22 * 2 = 44.
Therefore, the missing term is calculated by adding this new difference to the last known term: 42 + 44 = 86.

Option A: This value does not fit the identified pattern of two interleaved series where the difference doubles at each step.
Option B: This value does not follow the logical progression of the interleaved series. It might result from an arithmetic error or applying an incorrect pattern.
Option D: This value is incorrect. It may be the result of a miscalculation, such as incorrectly doubling the difference or applying a different, inconsistent rule.

Visual 1: Infographic: A flowchart illustrating the two interleaved series. One branch shows the progression of 12, 23, 45 with differences of +11 and +22. The second branch shows the progression of 20, 42, ? with differences of +22 and +44, leading to the answer 86.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Number Series Pattern Recognition as background academic context rather than a clinical decision trigger.
This type of logical reasoning question, while not directly clinical, assesses problem-solving and analytical skills that are crucial in nursing.
Nurses often need to identify patterns in patient symptoms, vital signs, and lab results to anticipate changes in a patient's condition.
Strong analytical skills help in making sound clinical judgments and prioritizing care effectively.

How to Approach the Question

First, examine the differences between consecutive numbers in the series: 12 to 20 (+8), 20 to 23 (+3), 23 to 42 (+19), 42 to 45 (+3).
Notice that a simple arithmetic or geometric progression does not fit. The repeating '+3' suggests a more complex, possibly alternating, pattern.
Test the hypothesis of two interleaved series. Separate the numbers into two groups based on their position: odd positions (1, 3, 5) and even positions (2, 4, 6).
Analyze the pattern for the odd-position series: 12, 23, 45. The differences are +11 and +22. This indicates the difference is doubling.
Analyze the pattern for the even-position series: 20, 42, ?. The first difference is +22.
Apply the doubling rule found in the first series to the second series. The next difference should be 22 * 2 = 44.

Concept Tested & Keywords

Q4i_pAMggHUfPGnXh0llRL

Practise the full NCL (Northern Coalfields Limited)-NO

Attempt every question from this paper in a timed mock, then review the full solution for each one.