Data Interpretation Formula Guide: Percentage Change, Pie Chart Angle, Ratio and Average Tricks for SSC
Rahul Kumar
SSC Exam Expert & Content Editor
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Data interpretation (DI) gives 3 to 5 questions in SSC CGL, and every question is based on four things: percentage, ratio, average and growth. This data interpretation formula guide for SSC gives the formulas, the pie chart angle rule and the quick tricks for tables, bar graphs and line graphs, with solved examples.
Main Formulas
| Item | Formula |
|---|---|
| Percentage change | (New − Old) / Old × 100 |
| Percentage | (Part / Whole) × 100 |
| Percentage point change | Difference of the two percentages (not a ratio) |
| Ratio | First value : Second value |
| Average | Total / Number of items |
| Pie chart angle of a part | (Value / Total) × 360° |
| Value from an angle | (Angle / 360) × Total |
Pie Chart Quick Table
| Percentage | Angle |
|---|---|
| 5% | 18° |
| 10% | 36° |
| 15% | 54° |
| 20% | 72° |
| 25% | 90° |
| 30% | 108° |
| 50% | 180° |
1% of the pie chart is 3.6°.
Type of Graph and What to Look For
| Graph | What to check |
|---|---|
| Table | Row and column totals, ratios between two cells |
| Bar graph | The height of the bars and the difference between two bars |
| Line graph | The rise and fall between two years |
| Pie chart | The angle or the percentage of each part |
Solved Examples
Example 1. Find the pie chart angle of a part that is 15% of the total.
15 × 3.6 = 54°.
Example 2. A value rises from 200 to 250. Find the percentage increase.
50/200 × 100 = 25%.
Example 3. A value falls from 250 to 200. Find the percentage decrease.
50/250 × 100 = 20%.
Example 4. The sales of a company in 2021, 2022 and 2023 are 120, 150 and 180. Find the average sales and the percentage growth from 2021 to 2022.
Average = 450/3 = 150. Growth = 30/120 × 100 = 25%.
Example 5. Find the ratio of the sales in 2021 to the sales in 2023 from the data above.
120 : 180 = 2 : 3.
Example 6. In a pie chart of a total of 1,200, a sector has an angle of 90°. Find its value.
90/360 × 1200 = 300.
Calculation Tricks
- Use fractions for percentages: 25% = 1/4, 20% = 1/5, 12.5% = 1/8, 16.67% = 1/6.
- Do not calculate the exact value when the options are far apart. Use an approximation.
- Compare the ratios by cross-multiplication and do not find the decimals.
- Read the title and the unit (thousands, lakhs, crores) of the graph first.
Quick Tips
- Read the unit and the title first.
- Use fractions for percentages.
- Approximate when the options are far apart.
- Remember 1% = 3.6° in a pie chart.
Quick Revision Points
- Percentage change = (New − Old)/Old × 100.
- Pie chart angle = (value/total) × 360°.
- 1% of a pie chart is 3.6°.
- Percentage point is the plain difference of two percentages.
- Compare the ratios by cross-multiplication.
Practice Questions With Answers
- What is the pie chart angle of 25%?
Answer: 90° - A pie chart sector has 72°. What percentage is it?
Answer: 20% - A value rises from 80 to 100. Find the percentage increase.
Answer: 25% - A value falls from 100 to 80. Find the percentage decrease.
Answer: 20% - Find the average of 120, 150 and 180.
Answer: 150 - Find the ratio of 120 to 180.
Answer: 2 : 3 - A sector has 120° in a pie chart of a total of 900. Find its value.
Answer: 300 - What is the percentage point difference between 30% and 24%?
Answer: 6 percentage points - What is the formula for percentage change?
Answer: (New − Old)/Old × 100 - How many degrees are there in a full pie chart?
Answer: 360°
How to Practise This Chapter
Write each formula on a card, with a solved example on the back, and revise the cards every day. Then test yourself with our practice papers and the previous year papers page. See all guides on the Formula Guide page, and also read the Mathematics notes and Quantitative Aptitude notes. The previous guide is Circle Geometry Theorems and the next guide is Squares, Cubes and Roots Table.
Frequently Asked Questions
What is data interpretation?
It is the reading of data from tables and graphs to answer questions.
What is the formula for percentage change?
(New − Old) divided by Old, multiplied by 100.
How do I find the angle of a part in a pie chart?
Multiply the percentage by 3.6, or use (value/total) × 360.
What is a percentage point?
It is the plain difference between two percentages.
How do I compare two ratios fast?
Use cross-multiplication.
Should I find exact values in DI?
No. Approximate when the options are far apart.
What is the use of fractions in DI?
They make the percentage calculations faster.
Is DI asked in SSC exams?
Yes. DI is asked in SSC CGL and CHSL maths.
How much time should I take?
About 40 to 60 seconds for each question of a set.
What are common mistakes?
Not reading the unit and using the wrong base for the percentage.
How can I improve my speed?
Learn the fraction table and practise one DI set daily.
What is average growth?
The average of the growth rates of each year.
Previous chapter
Circle Geometry Theorems and Formulas: Chords, Tangents, Cyclic Quadrilateral and Common Tangents for SSC
Next chapter
Squares, Cubes, Square Roots and Powers Table: 1 to 30 Squares and 1 to 15 Cubes for SSC Maths
Rahul Kumar
SSC Exam Expert & Content Editor
Rahul is a senior SSC exam strategist with 8+ years of experience helping aspirants crack CGL, CHSL and MTS exams. He writes in-depth notification breakdowns, exam pattern guides and preparation strategies.