The average of 15, 17, 19 and 21 is?

Appeared in: DHS Staff Nurse - 2018 (Shift-2nd)

Explanation

The average (or mean) is the sum of the values divided by the number of values.
Sum of the numbers: 15 + 17 + 19 + 21 = 72.
Number of values: 4.
Average = 72 / 4 = 18.
Alternatively, for an arithmetic sequence like this (common difference of 2), the average is the midpoint, which is also the average of the first and last term: (15 + 21) / 2 = 18.

Option A: 17 is the second number in the sequence, not the average of all four numbers.
Option B: 20 is an incorrect calculation. It might be a guess or a miscalculation.
Option C: 21 is the largest number in the sequence, not the average.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Calculation of the arithmetic mean (average) of a set of numbers as background academic context rather than a clinical decision trigger.
Calculating averages is a fundamental skill in nursing for interpreting patient data trends, such as averaging a week's worth of blood glucose readings to assess glycemic control.
Nurses use mean arterial pressure (MAP), an average of blood pressure during a single cardiac cycle, to assess organ perfusion. A MAP of at least 60 mmHg is typically needed.
What if? If a patient's fluid intake over 4 hours was 150 mL, 170 mL, 190 mL, and 210 mL, the average hourly intake would be (150+170+190+210)/4 = 180 mL/hr, which is crucial for monitoring fluid balance.

How to Approach the Question

First, identify the task: the question asks for the 'average' of a given set of numbers.
Recall the definition of average (mean): it is the sum of all values divided by the count of the values.
Step 1: Add all the numbers together: 15 + 17 + 19 + 21.
Step 2: Count how many numbers are in the set (in this case, 4).
Step 3: Divide the sum from Step 1 by the count from Step 2 to find the final answer.
Check if there's a shortcut. Since the numbers are evenly spaced, the average is simply the average of the first and last numbers: (15 + 21) / 2.

Concept Tested & Keywords

Concept Tested: Calculation of the arithmetic mean (average) of a set of numbers.
Stem keywords: average, 15, 17, 19, 21
Lead-in keywords: is?

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