Mastering GRE Data Interpretation: Charts & Graphs
This guide provides a systematic approach to GRE Quantitative Data Interpretation from charts, focusing on what examiners test, a step-by-step method, a worked example, common pitfalls, and a quick recap.
What the Examiner is Testing
The GRE Quantitative section uses data interpretation questions to assess your ability to extract relevant information from visual representations and then apply mathematical reasoning to solve problems. This evaluates both your numerical literacy and your analytical problem-solving skills under timed conditions.
The Method: A Step-by-Step Approach
Follow these steps consistently to maximize your accuracy and efficiency on data interpretation questions:
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Understand the Question First: Before even looking at the chart, read the question carefully. Identify exactly what information is being requested and what units are involved. This prevents you from getting lost in irrelevant data.
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Scan the Chart for Overall Context:
- Title and Subtitle: What is the chart about? What is the main theme or subject?
- Axes Labels and Units: What do the x and y axes represent? What are their units (e.g., millions of dollars, percentage, number of units)? Pay close attention to powers of ten (e.g., "in thousands").
- Legend/Key: If there are multiple data series or categories, understand what each color, line style, or pattern signifies.
- Source/Footnotes: While less common on the GRE, these can sometimes provide crucial context or limitations.
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Locate Relevant Data Points: Based on your understanding of the question, pinpoint the specific data points or sections of the chart that are needed. Don't try to absorb everything at once.
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Extract and Transcribe Data: Carefully read the values associated with the identified data points. If necessary, write them down to avoid mental errors, especially for multi-step calculations. Double-check units and scaling factors.
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Perform Calculations: Execute the mathematical operations required by the question. This might involve:
- Ratios/Proportions: "What fraction of X is Y?"
- Percentages: "What is the percentage increase/decrease?"
- Averages: "What is the mean/median value?"
- Absolute Differences: "How much more/less is X than Y?"
- Extrapolation/Interpolation (rare, but possible): Estimating values beyond or between given data points.
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Review and Verify:
- Does the answer make sense in context? A quick sanity check can catch major errors (e.g., a percentage increase being larger than 100% when it shouldn't be).
- Did you answer the exact question asked? (e.g., "percentage increase" vs. "final percentage").
- Are the units correct?
Fully Worked Example
Consider the following hypothetical bar chart showing the annual revenue (in millions of USD) for TechCorp's three product lines (A, B, C) from 2018 to 2020.
Chart: Annual Revenue for TechCorp Product Lines (2018-2020)
| Year | Product A (Millions USD) | Product B (Millions USD) | Product C (Millions USD) |
|---|---|---|---|
| 2018 | 120 | 80 | 50 |
| 2019 | 150 | 90 | 60 |
| 2020 | 180 | 100 | 70 |
Question: What was the approximate percentage increase in the total combined revenue of Product A and Product C from 2018 to 2020?
Solution:
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Understand the Question First: We need the percentage increase in total combined revenue for Product A and Product C from 2018 to 2020.
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Scan the Chart for Overall Context: The chart shows annual revenue in millions of USD for three product lines over three years. Units are in millions.
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Locate Relevant Data Points:
- Product A revenue in 2018
- Product C revenue in 2018
- Product A revenue in 2020
- Product C revenue in 2020
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Extract and Transcribe Data:
- Product A (2018): 120 million USD
- Product C (2018): 50 million USD
- Product A (2020): 180 million USD
- Product C (2020): 70 million USD
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Perform Calculations:
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Combined Revenue 2018:
\(R_{2018} = R_{A,2018} + R_{C,2018} = 120 \text{ million USD} + 50 \text{ million USD} = 170 \text{ million USD}\) -
Combined Revenue 2020:
\(R_{2020} = R_{A,2020} + R_{C,2020} = 180 \text{ million USD} + 70 \text{ million USD} = 250 \text{ million USD}\) -
Percentage Increase Formula:
$$\text{Percentage Increase} = \frac{\text{New Value} - \text{Original Value}}{\text{Original Value}} \times 100\%$$ -
Calculate Percentage Increase:
$$\text{Percentage Increase} = \frac{250 \text{ million USD} - 170 \text{ million USD}}{170 \text{ million USD}} \times 100\%$$
$$\text{Percentage Increase} = \frac{80}{170} \times 100\%$$
$$\text{Percentage Increase} \approx 0.47058 \times 100\%$$
$$\text{Percentage Increase} \approx 47.06\%$$
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Review and Verify: A 47% increase from 170 to 250 seems reasonable. The question asked for percentage increase, not the final value. Units are consistent.
The approximate percentage increase is \(47.06\%\).
Three Mistakes That Lose Marks
- Misinterpreting Units or Scale: Failing to account for "in thousands," "millions," or incorrectly reading the axis scale (e.g., assuming linear progression when it's logarithmic, or misreading tick marks). This is a fundamental error that leads to wildly incorrect answers.
- Answering the Wrong Question: Calculating the total revenue when asked for the average, or finding the absolute difference when a percentage change is required. Always re-read the question after calculating to ensure your answer directly addresses it.
- Careless Calculation Errors: Simple arithmetic mistakes, especially under time pressure. This includes errors in addition, subtraction, multiplication, division, or misplacing a decimal. Writing down intermediate steps and performing quick mental checks can help mitigate this.
A 30-Second Recap
Always read the question first to know what you're looking for. Then, quickly grasp the chart's context, units, and legend. Extract only the necessary data points, perform calculations carefully, and always double-check your answer against the original question and for reasonableness. Avoid unit/scale errors, answering the wrong question, and arithmetic mistakes.