Complete the series-50, 40, 30......, 10?

Appeared in: HSSC Staff Nurse - 2015

Explanation

The question presents a number series where each number decreases by a constant amount.
The pattern is an arithmetic progression with a common difference of -10 (each number is 10 less than the previous one).
Starting from 30, the next term is calculated by subtracting 10, which gives 20.
This is confirmed by the subsequent term, as 20 minus 10 equals 10, the final number in the series.

Option A: The number 30 is the term immediately preceding the missing number in the series, not the missing number itself.
Option C: Selecting 25 would imply a difference of -5 from the previous term (30 - 5 = 25), which is inconsistent with the established pattern of subtracting 10.
Option D: The number 60 is greater than the starting number of the series. The series is clearly in a decreasing order, so an increasing number is incorrect.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Arithmetic Progression in Number Series as background academic context rather than a clinical decision trigger.
This question assesses logical reasoning and pattern recognition, which are fundamental cognitive skills.
While not a clinical question, these skills are crucial for nurses in tasks like interpreting trends in vital signs, calculating medication dosages, and identifying changes in a patient's condition over time.
What if the series was 50, 40, 31, 23...? The pattern would no longer be a simple arithmetic progression. One would need to look for a different pattern, such as subtracting increasing numbers (e.g., -10, -9, -8), requiring more complex analytical skills.

How to Approach the Question

First, carefully observe the sequence of numbers provided: 50, 40, 30, ..., 10.
Calculate the difference between the first two consecutive terms: 40 - 50 = -10.
Calculate the difference between the next pair of consecutive terms to confirm the pattern: 30 - 40 = -10.
Identify the rule governing the series. In this case, each term is obtained by subtracting 10 from the previous term.
Apply this rule to the last known term before the blank space: 30 - 10 = 20.
Verify your answer by applying the rule one more time to see if it results in the next number in the series: 20 - 10 = 10. This matches, confirming 20 is the correct missing term.

Concept Tested & Keywords

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