# Data Interpretation — Bar Graphs, Tables and Pie Charts

Source: https://skills101.in/learn/aptitude/data-interpretation — Skills101 free tutorial (Quantitative Aptitude). Updated 2026-11-09.

Data Interpretation (DI) gives you a chart or table and 4–5 questions on it. It tests **percentages, ratios and averages** — everything from earlier lessons — on real-looking data.

## The 4-step method

1. **Read the title, units and labels first.** "In hundreds"? "In ₹ lakh"? "Percentage of total"? Missing the unit is the most common mistake.
2. **Read the question carefully.** Which year? Which item? Growth from what to what?
3. **Write down only the numbers you need.**
4. **Approximate** when the options are far apart.

## 1. Bar graphs

![Bar graph of laptops sold in hundreds: 2021 = 4, 2022 = 6, 2023 = 5, 2024 = 9. Growth from 2023 to 2024 is 80%](https://skills101.in/learn-img/aptitude/di-bar.svg)

Use the chart above for these:

### Example 1
*How many laptops were sold in total in the four years?*

(4 + 6 + 5 + 9) hundred = 24 hundred = **2,400**.

### Example 2
*What is the percentage growth from 2023 to 2024?*

(9 − 5) ÷ 5 × 100 = **80%**. (Divide by the **earlier** year.)

### Example 3
*In which year was the percentage change from the previous year the largest?*

- 2022: +2 on 4 = +50%
- 2023: −1 on 6 = −16.7%
- 2024: +4 on 5 = **+80%** → **2024**

### Example 4
*What is the average number sold per year?* 2,400 ÷ 4 = **600**.

## 2. Tables

| Department | Employees | Women (%) |
|---|---|---|
| Sales | 200 | 30% |
| Tech | 300 | 25% |
| HR | 50 | 60% |

### Example 5
*How many women work in Tech?* 25% of 300 = **75**.

### Example 6
*What percentage of all employees are women?*

Women: 60 + 75 + 30 = 165. All: 550. 165 ÷ 550 × 100 = **30%**.

(Notice it is **not** the average of 30, 25 and 60 — the departments are different sizes.)

## 3. Pie charts

A pie chart shows **parts of a whole**. The whole circle is **100%** or **360°**.

> **Angle = (percentage ÷ 100) × 360°**, so 1% = 3.6°.

### Example 7
*A family spends ₹40,000 a month. Rent is 25% of the pie. How much is rent, and what angle is its slice?*

Rent = 25% of 40,000 = **₹10,000**. Angle = 25 × 3.6 = **90°**.

### Example 8
*In the same pie, food is 72°. What is the food budget?*

72° ÷ 3.6 = 20% → 20% of 40,000 = **₹8,000**.

## 4. Line graphs

A line graph shows a value over time. The **steepest** upward segment is the biggest **absolute** increase — but not always the biggest **percentage** increase (a rise of 10 on a base of 20 is 50%, but a rise of 15 on 100 is only 15%).

## Speed tips

- Ratios and comparisons often need **no calculation** — compare the bars by eye first.
- For "approximately", round to easy numbers.
- If several questions use the same total, calculate it **once** and write it down.

## Common mistakes

- Ignoring units ("in hundreds", "in lakhs").
- Dividing by the later value in growth % (always divide by the **earlier** value).
- Averaging percentages from groups of different sizes.

## Quick recap

- Title, units, labels → question → numbers → approximate.
- Growth % = change ÷ earlier value × 100.
- Pie: 100% = 360°, 1% = 3.6°.
- Combined % = total part ÷ total whole, not the average of the %s.


Practice quiz and free certificate: https://skills101.in/learn/aptitude/data-interpretation