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Calculating Averages
Finding the arithmetic mean by summing values and dividing by count.
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Finding the arithmetic mean by summing values and dividing by count.
The arithmetic mean (average) is found by adding all values and dividing by the number of values. It represents the 'typical' value in a dataset. When reading charts, you may need to extract all values first, then calculate. The average is sensitive to outliers—one very high or low value can shift it significantly.
average = (sum of all values) / (number of values)
- Values: 10, 20, 30, 40 → Average = 100/4 = 25
- Bar chart with heights 50, 60, 80, 90, 70 → Average = 350/5 = 70
- Monthly sales: Jan=100, Feb=120, Mar=110 → Average = 330/3 = 110
How to recognize it
- Questions asking for 'average', 'mean', or 'typical value'
- Need to combine multiple data points into one summary
- Comparing overall performance across categories
Common mistakes
- Dividing by wrong count (missing or extra values)
- Adding incorrectly before dividing
- Confusing average with median or mode
Step-by-step walkthrough
The bar chart shows monthly sales for 5 regions. What is the average sales value?
- Read each bar's value from the chart: North=50, South=60, East=80, West=90, Central=70
- Add all values together: 50 + 60 + 80 + 90 + 70 = 350
- Count the number of bars: 5 regions
- Apply the average formula: Sum ÷ Count = 350 ÷ 5
- Calculate: 350 ÷ 5 = 70
Answer: 70 units
Practice guidance
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