In this guide
Data interpretation (DI) usually arrives as one chart followed by a few questions. The maths is basic: percentages, ratios and averages. Marks are lost in two ways. Candidates misread the chart (the wrong bar, the wrong unit, the wrong year), or they calculate slowly because they redo the same total for every question.
In Tier 1, a DI set may or may not appear in your shift; in Tier 2 it is more likely, sometimes with longer tables. Either way, the method is the same. Read the title, the units and the axes before you read a single question.
The calculations, and why they work
- Percentage change = (new − old)/old × 100. The base is always the earlier or reference value, because "change" is measured against where you started.
- Share = part/total × 100. Find the total once and reuse it.
- Ratio = one value : another, simplified by the HCF.
- Average = total ÷ number of items.
- Pie chart in degrees: percentage = degrees/360 × 100, so 3.6° = 1%. Why: the whole circle, 360°, is 100%.
- Pie chart to amounts: amount = degrees/360 × total. If the total is ₹60,000, each degree is worth ₹60,000/360.
Keep a small fraction table in mind: 1/8 = 12.5%, 1/6 = 16⅔%, 1/3 = 33⅓%, 3/8 = 37.5%. DI answers often land exactly on these.
Percent versus percentage points
If a share rises from 20% to 25%, it has risen by 5 percentage points but by 25 percent (5/20 × 100). Questions sometimes test exactly this difference. Read which one is asked.
Set 1: a bar graph
The bar graph shows a shop's sales. The values are given here as a table.
Sales of a shop (₹ thousand)
| Month | Jan | Feb | Mar | Apr | May |
|---|---|---|---|---|---|
| Sales | 40 | 50 | 45 | 60 | 55 |
Q1. What is the average monthly sale?
Total = 40 + 50 + 45 + 60 + 55 = 250. Average = 250 ÷ 5 = ₹50 thousand.
Q2. In which months did sales fall compared with the previous month?
March (50 → 45) and May (60 → 55). Answer: March and May.
Set 2: a pie chart
A family's monthly expenditure of ₹60,000 is shown in a pie chart. Each degree is worth ₹60,000/360.
| Item | Degrees | Percentage | Amount (₹) |
|---|---|---|---|
| Food | 108° | 30% | 18,000 |
| Rent | 72° | 20% | 12,000 |
| Education | 54° | 15% | 9,000 |
| Transport | 36° | 10% | 6,000 |
| Savings | 45° | 12.5% | 7,500 |
| Others | 45° | 12.5% | 7,500 |
In the exam you will see only the degrees. The last two columns show what you should be able to work out in your head.
Q3. How much does the family spend on food?
108/360 = 3/10, and 3/10 × 60,000 = ₹18,000.
Q4. How much more is spent on rent than on transport?
The gap is 72° − 36° = 36°, which is 10% of 60,000 = ₹6,000. Work with the degree difference instead of finding both amounts.
Set 3: a two-row table
Units produced (thousand) by two factories
| Year | 2021 | 2022 | 2023 | 2024 |
|---|---|---|---|---|
| Factory A | 120 | 150 | 180 | 165 |
| Factory B | 100 | 110 | 140 | 160 |
Q5. In which year was the combined production highest?
Totals: 220, 260, 320, 325. Answer: 2024, by a small margin over 2023. Close totals like this are why you write them down rather than eyeball the bars.
Q6. Find the ratio of A's total production over the four years to B's.
A = 615, B = 510. HCF 15: 41 : 34.
Approximation
When options are far apart, round early. 38.7% of 812 is about 39% of 800, roughly 312. When options are close (say 24.2% and 24.8%), calculate exactly. Look at the options before you decide how precise to be.
Common traps
| Trap | Fix |
|---|---|
| Ignoring units (thousands, lakhs, crores) | Read the chart heading and axis labels |
| Wrong base for percentage change | The earlier value is the base |
| Reading the wrong bar or row | Put a finger or the mouse pointer on the row |
| Confusing degrees with percentages | Convert with 3.6° = 1% |
| Mixing percent and percentage points | Check which one the question asks |
| Recalculating totals for each question | Write totals once |
Strategy in the exam
- Read the chart title, units and all the questions first.
- Write the totals you will need.
- Look at the options before calculating, and approximate when they are far apart.
- If the set looks long and time is short, move it to your second pass instead of abandoning it.
Practice
Questions 1–2 use Set 1, 3–5 use Set 2, and 6–8 use Set 3.
- What is the percentage increase in sales from March to April?
- What percentage of the five-month total was sold in April?
- How much does the family save each month, and what percentage of spending is on education?
- Find the ratio of spending on food to spending on education.
- If monthly spending rises to ₹72,000 with the same proportions, how much goes on rent?
- Find the percentage decrease in A's production from 2023 to 2024.
- In which year was B's production the highest percentage of A's?
- Find A's average annual production over the four years.
Answers:
- 33⅓%. (60 − 45)/45 × 100 = 15/45 × 100.
- 24%. 60/250 × 100.
- ₹7,500 and 15%. 45/360 × 60,000; 54/3.6.
- 2 : 1. 108 : 54.
- ₹14,400. 20% of 72,000.
- 8⅓%. 15/180 × 100.
- 2024. 160/165 is about 97%; the other years are 83%, 73% and 78%.
- 153.75 thousand units. 615 ÷ 4.
What to do next
- Solve one DI set a day for two weeks, timing each set.
- Practise converting pie-chart degrees to percentages until 3.6° = 1% is automatic.
- Write totals before questions in every set, even easy ones.
- Revise percentages and averages, which do most of the work in DI.
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 Staff Selection Commission website .
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