Find the missing term. 21, 25, 29....., 37?

Appeared in: HSSC Staff Nurse - 2015

Explanation

The question presents an arithmetic progression, which is a sequence of numbers where the difference between consecutive terms is constant.
By subtracting any term from its subsequent term (e.g., 25 - 21 = 4; 29 - 25 = 4), we find a common difference of +4.
To find the missing term, the common difference of 4 is added to the preceding term, 29.
Calculation: 29 + 4 = 33.
This is confirmed by the next term in the sequence: 33 + 4 = 37.

Option B: Choosing 31 would imply a common difference of 2 (31 - 29 = 2), which breaks the established pattern of adding 4.
Option C: Choosing 30 would imply a common difference of 1 (30 - 29 = 1), which is inconsistent with the series' pattern of adding 4.
Option D: Choosing 34 would imply a common difference of 5 (34 - 29 = 5), which does not follow the consistent pattern of adding 4.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Number Series and Arithmetic Progression as background academic context rather than a clinical decision trigger.
While not a clinical question, this type of logical reasoning and basic arithmetic is a foundational skill for nursing.
It is directly applicable in clinical practice for tasks such as calculating medication dosages, titrating IV drips, and interpreting data trends on patient charts.
For example, if a patient's fluid output is measured hourly and shows a consistent increase, a nurse uses this same pattern-recognition skill to anticipate trends and report potential issues.

How to Approach the Question

First, identify the question type, which is a 'find the missing term' in a number series.
Examine the relationship between the first few numbers to find a pattern. Calculate the difference between consecutive terms: 25 - 21 = 4 and 29 - 25 = 4.
Recognize that the pattern is an arithmetic progression with a constant difference of +4.
Apply this pattern to the last known term before the gap: 29 + 4 = 33.
Verify your answer by applying the pattern one more time to see if it matches the next term in the sequence: 33 + 4 = 37. It does.
Select the option that matches your calculated result.

Concept Tested & Keywords

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Practise the full HSSC Staff Nurse - 2015

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