Find the missing number in the following number series?
5.69, 4.56, 3.43, ____, 1.17

Appeared in: DSSSB - 29 August 2019 (Shift-2)

Explanation

The series follows a pattern of subtracting a constant value from each term to get the next.
The difference between consecutive terms is calculated as 1.13 (e.g., 5.69 - 4.56 = 1.13 and 4.56 - 3.43 = 1.13).
This type of sequence is known as an arithmetic progression with a common difference of -1.13.
To find the missing term, subtract 1.13 from the preceding term: 3.43 - 1.13 = 2.30.
To confirm, the next term is calculated as 2.30 - 1.13 = 1.17, which matches the final number in the series.

Option B: If 2.21 were the missing term, the difference from the previous term (3.43) would be 1.22, which is inconsistent with the established common difference of 1.13.
Option C: Choosing 2.17 would mean the difference is 3.43 - 2.17 = 1.26. This breaks the consistent pattern of subtracting 1.13.
Option D: If 2.15 were the term, the difference would be 3.43 - 2.15 = 1.28. This deviates from the common difference of 1.13 and disrupts the arithmetic progression.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Arithmetic Progression in a Number Series as background academic context rather than a clinical decision trigger.
While this is a mathematics question, the underlying skill of logical reasoning and pattern recognition is vital in nursing.
Nurses use analytical skills to interpret trends in vital signs, lab results, and patient symptoms over time.
Accurate calculation is a fundamental safety skill for medication administration, including dosage calculations and IV drip rate titration.

How to Approach the Question

First, examine the relationship between the first few numbers to identify a potential pattern. Notice that the numbers are decreasing.
Calculate the difference between the first and second terms: 5.69 - 4.56 = 1.13.
Calculate the difference between the second and third terms to confirm the pattern: 4.56 - 3.43 = 1.13.
Since the difference is constant, you have identified an arithmetic progression where 1.13 is subtracted at each step.
Apply this rule to find the missing term: subtract 1.13 from the last known term before the blank, which is 3.43. The result is 2.30.
As a final check, apply the rule one more time to your result to see if it produces the next term in the series: 2.30 - 1.13 = 1.17. It matches.

Concept Tested & Keywords

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