Introduction to Data Interpretation: Tables and Bar Graphs
What is Data Interpretation (DI)?
DI questions give data in a table, bar graph, pie chart or line graph and ask you to calculate totals, averages, ratios and percentage changes.
Sample data: bike sales (thousands)
| Year | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|
| Sales | 40 | 50 | 45 | 60 | 55 |
- Total = 250; average = 250 ÷ 5 = 50 thousand.
- % change 2023 → 2024 = (60 − 45)/45 × 100 = 33.33%.
- Ratio 2021 : 2024 = 40 : 60 = 2 : 3.
Bar graphs
Each bar's length/height shows the value. Read the scale carefully; compare bars before calculating.
Core formulas
- % change = (New − Old)/Old × 100
- Average = Total ÷ Number of items
- Share % = Part/Total × 100
Exam tips (RRB NTPC)
- Read the title, units (thousands, lakh, ₹ crore) and years before solving.
- Approximate when options are far apart.
Analogy
A data table is like a railway timetable. You don't read every line — you find the right row (train) and column (station), then do a quick calculation such as journey time. DI works the same way: locate the right cells first, then calculate.
Tests for this lesson
- Introduction to Data Interpretation: Tables and Bar Graphs practice
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