In this guide
GS Paper I of BPSC Mains includes statistical analysis, graphs and diagrams. For candidates with a science or commerce background, this is familiar territory. For many humanities graduates, it is the section they dread — and some skip it entirely. That is a costly mistake. Unlike essay-type answers, where marks depend on the examiner's judgement, a correct calculation usually earns full marks.
What is tested
The level is roughly that of Classes 10–12. Typical tasks include:
- finding mean, median and mode;
- calculating percentages, ratios, growth rates and averages;
- reading data from a table, bar chart, pie chart or line graph;
- drawing a bar diagram, pie chart or line graph from given data;
- simple interpretation — which item increased most, what share a category has.
Core concepts
Measures of central tendency
| Measure | Definition | Example (data: 4, 6, 6, 8, 11) |
|---|---|---|
| Mean | Sum ÷ number of items | (4+6+6+8+11) ÷ 5 = 35 ÷ 5 = 7 |
| Median | Middle value when arranged in order | 6 |
| Mode | Most frequent value | 6 |
For an even number of items, the median is the average of the two middle values.
Weighted mean: Σ(value × weight) ÷ Σ(weights). Useful for averages of groups of different sizes.
Percentages and growth
- Percentage = (part ÷ whole) × 100.
- Growth rate = (new − old) ÷ old × 100.
- Percentage point vs per cent: a rise from 10% to 12% is 2 percentage points but a 20 per cent increase.
Ratios
- To divide 600 in the ratio 2 : 3 → 240 and 360.
Worked example 1: a table
A district's crop production (thousand tonnes):
| Crop | Year 1 | Year 2 |
|---|---|---|
| Rice | 200 | 230 |
| Wheat | 150 | 150 |
| Maize | 100 | 130 |
Q: Which crop grew fastest, and what was total growth?
- Rice: 30 ÷ 200 = 15%; Wheat: 0%; Maize: 30 ÷ 100 = 30% → maize grew fastest.
- Total: 450 → 510; growth = 60 ÷ 450 × 100 ≈ 13.3%.
Worked example 2: pie chart
A household spends ₹20,000 a month: food ₹8,000, rent ₹5,000, education ₹3,000, others ₹4,000. Draw a pie chart.
Angle for each item = (value ÷ total) × 360°:
| Item | Share | Angle |
|---|---|---|
| Food | 40% | 144° |
| Rent | 25% | 90° |
| Education | 15% | 54° |
| Others | 20% | 72° |
Check: 144 + 90 + 54 + 72 = 360°.
Drawing diagrams well
- Use a scale and a ruler; label axes (with units).
- Give a title.
- For bar diagrams, keep bar widths equal and gaps equal.
- For pie charts, use a protractor if allowed; otherwise draw carefully and label each sector with its angle and percentage.
- For line graphs, mark points clearly and join them with straight lines.
- Add a short interpretation below — one or two sentences on what the diagram shows.
Common errors
| Error | Fix |
|---|---|
| Growth calculated on the new value | Always divide by the old value |
| Confusing percentage points and per cent | Be explicit |
| Angles not adding to 360° | Check totals |
| No units or labels | Always label |
| Arithmetic slips under time pressure | Practise; double-check key steps |
Using data elsewhere in the Mains
The skills in this section also help in other answers — citing and interpreting Bihar Economic Survey data (growth, sectoral shares, credit–deposit ratio) makes GS II answers much stronger.
A practice plan
| Weeks | Practice |
|---|---|
| 1–2 | Mean, median, mode; percentages and ratios — 20 problems a session |
| 3–4 | Tables and growth rates; bar diagrams |
| 5–6 | Pie charts and line graphs; interpretation sentences |
| Ongoing | One section from a previous paper every week, timed |
Two short sessions a week for two months are usually enough to make this section a reliable source of marks.
A note on dates and numbers. Exam patterns, vacancies and schedules change from year to year. Always confirm the current details in the latest notification on the Bihar Public Service Commission website .
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