TNPSC Group II · Bite-size lessons
Data Interpretation
About 7 min · Aptitude and Mental Ability · English
Time worked out from the lesson's 497 words at 150 words a minute, plus a minute for each question.
Data Interpretation (DI) tests your ability to extract, analyse and calculate information from organised data. Unlike pure arithmetic, DI requires you to read visual or tabular data correctly before applying calculations — a two-step skill that many candidates underestimate.
Key ideas
- Data formats: Tables present exact numbers in rows and columns; Bar graphs show comparisons across categories; Line graphs display trends over time; Pie charts show part-to-whole relationships (always totalling 100% or 360°).
- Reading the question first: Before studying the entire data set, read what is asked. This saves time by focusing your attention on relevant rows, columns, or segments only.
- Percentage of a whole: In pie charts, each sector = (sector value / total) × 100. Conversely, if percentage is given, value = (percentage / 100) × total.
- Percentage change: Always calculated as [(New − Old) / Old] × 100. A common trap is dividing by the new value instead.
- Ratio from data: To compare two quantities, express them as a fraction and simplify. Ratios can be read directly from bar heights or table values.
Watch out for
- Dividing by the wrong base for percentage change → Always divide by the old (original) value, not the new one. "Percentage increase from X" means X is the base.
- Misreading pie chart totals → Students assume the total is 100 when it might be given as an absolute number (like ₹2,00,000). Always check what the total represents.
- Ignoring units → Data may be in '000 units, lakhs, or crores. Failing to account for this leads to answers off by a large factor (1,000 for '000 units, 1,00,000 for lakhs, 1,00,00,000 for crores).
Quick reference
- Percentage change = (Difference / Original) × 100 — always divide by old value
- Pie chart: 1% = 3.6°; so 25% = 90°, 50% = 180°
- For quick division: 1/4 = 25%, 1/5 = 20%, 1/8 = 12.5%
- Read the question before analysing the entire data set
- Approximate boldly
Check yourself: 3 questions
1. The following table shows the number of students enrolled in five different courses at a coaching centre over three years. Course | 2021 | 2022 | 2023 -------|------|------|------ Maths | 120 | 150 | 180 Science| 100 | 110 | 130 English| 90 | 95 | 100 History| 80 | 85 | 90 Geography| 70 | 75 | 80 What is the total number of students enrolled in all courses in 2022?
2. A bar graph shows the production of rice (in thousand tonnes) in five districts of Tamil Nadu in 2023: Thanjavur: 80 Trichy: 60 Nagapattinam: 70 Thiruvarur: 50 Pudukkottai: 40 What is the percentage of rice production in Thanjavur compared to the total production across all five districts?
3. A pie chart shows the distribution of a family's monthly expenditure of Rs. 40,000: Food: 30% Rent: 25% Education: 20% Transport: 15% Others: 10% If the expenditure on Food increases by 20% and all other expenditures remain the same, what will be the new total monthly expenditure?
This lesson is cut from the topic's note, not rewritten. Fact-checked on 17 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.
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