Data interpretation for SSC CGL

Data interpretation looks like the hardest part of the maths section, because a chart and five questions take up a whole screen. It is actually one of the most learnable. The maths never goes beyond percentages, ratios and averages. What separates a good score from a poor one is reading the chart correctly and not calculating more than the question needs.

This guide covers how DI appears in SSC CGL, the small toolkit of calculations, three fully worked sets (a table, a line graph and a pie chart) and a practice set with solutions.

How DI appears in SSC CGL

In Tier 1, the maths section has 25 questions of 2 marks each, with 0.50 deducted for a wrong answer, and Tier 1 is qualifying. In Tier 2 Paper I, maths has 30 questions of 3 marks each (90 of the 390 scored marks), and a wrong answer costs a full mark.

DI shows up in both tiers, either as a set of a few questions on one chart or as single questions on a small table or graph. The number of DI questions varies from shift to shift, so don't plan around a fixed count. Plan around the fact that a DI set rewards one careful reading: if you read the chart well once, three or four questions fall quickly.

Know your chart

In this post the bar and line graphs are written as tables of the values you would read off them. In the exam, spend five seconds on the axis before touching a question: a scale in thousands or crores changes every answer.

The calculation toolkit

• Percentage change = (new − old)/old × 100. The old value is the base.
• Share = part/total × 100.
• Ratio of two values, simplified.
• Average = total/number of items.
• Pie conversions: degrees to percentage = degrees/360 × 100, so 3.6° = 1%, 36° = 10%, 90° = 25%. Percentage to degrees: multiply by 3.6.

Percentage points vs percentage change

Suppose the bus share of a school's students falls from 40% to 35%. That is a fall of 5 percentage points, but a 12.5% fall in the share (5/40 × 100). Questions that say "by what percent did the share fall" want 12.5%. This is the single most common reading error in DI.

Fractions you should know as percentages

With this table, 36/130 is close to 36/132 = 3/11 ≈ 27.3%, and the exact value (27.7%) is a quick check away. An increase from 80 to 92 is 12/80 = 3/20 = 15%.

Approximation

When options are far apart, round early. 4,87,000 is about 4.9 lakh and 2,03,000 about 2.0 lakh, so their ratio is about 2.4 (the exact value is 2.399). When options are close, as they often are in Tier 2, round only the last step.

Worked set 1: a table

Production of cars (in thousands) by a company:

The total column is not given in most exam tables. Add it yourself first; three of the five questions below use it.

Q1. What is the percentage increase in Model A's production from 2021 to 2024?
(60 − 40)/40 × 100 = 50%.

Q2. In which year was total production highest?
From the total column: 2024 (150 thousand).

Q3. What percentage of total production in 2023 was Model B?
36/130 × 100 ≈ 27.7%.

Q4. What is the average annual production of Model C?
(35 + 45 + 44 + 50)/4 = 174/4 = 43.5 thousand.

Q5. What is the ratio of Model A's total production to Model B's over the four years?
A = 40 + 45 + 50 + 60 = 195; B = 25 + 30 + 36 + 40 = 131. Ratio = 195 : 131 (131 is prime and does not divide 195, so this is already in lowest terms).

Worked set 2: a line graph

Revenue and expenditure of a firm (₹ crore), as read from a line graph:

Profit = revenue − expenditure; again, write the column once.

Q1. In which year was the percentage increase in revenue over the previous year the highest?
2021: 30/80 = 37.5%. 2022: a fall. 2023: 30/100 = 30%. 2024: 40/130 ≈ 30.8%. The answer is 2021, even though the biggest jump in rupees (₹40 crore) came in 2024. A steep-looking segment on a graph is not always the biggest percentage rise; the base matters.

Q2. What is the average annual expenditure over the five years?
(70 + 90 + 85 + 100 + 130)/5 = 475/5 = ₹95 crore.

Q3. Total profit over the five years is what percentage of total revenue?
Total profit = 10 + 20 + 15 + 30 + 40 = 115. Total revenue = 80 + 110 + 100 + 130 + 170 = 590. 115/590 × 100 ≈ 19.5%.

Q4. What is the ratio of revenue in 2022 to expenditure in 2024?
100 : 130 = 10 : 13.

Worked set 3: a pie chart

Mode of transport of 1,200 students of a school (percentages): bus 35%, walking 20%, private car 18%, cycle 15%, auto-rickshaw 12%. (Check: 35 + 20 + 18 + 15 + 12 = 100.)

Q1. How many students come by bus? 35% of 1,200 = 420.

Q2. What is the central angle for cycle? 15 × 3.6 = 54°.

Q3. How many more students come by bus than by car? (35 − 18)% of 1,200 = 17% of 1,200 = 204. Subtract the percentages first; it saves one multiplication.

Q4. What is the ratio of walkers to auto-rickshaw users? 20 : 12 = 5 : 3. No need to convert to numbers at all, because both are shares of the same total.

Common traps

Strategy in the exam

1. Read the chart and all the questions first. One total or one column of differences often answers two questions.
2. Write totals and differences once on your rough sheet and reuse them.
3. Approximate when options are well apart; calculate exactly when they are close.
4. Leave long sets for the second round if the section still has quick questions waiting. In Tier 2, a wrong answer costs a full mark, so a rushed DI set is expensive.

Practice

Use the three sets above.

1. What is the percentage increase in total car production from 2022 to 2024?
2. Which car model had the highest percentage growth from 2021 to 2024?
3. What is Model C's share of total car production in 2022?
4. By what percentage was Model A's 2023 production more than Model B's?
5. In set 2, what was the firm's profit as a percentage of expenditure in 2023?
6. In set 2, by what percentage did expenditure rise from 2020 to 2024?
7. In set 3, what is the central angle for walking, and how many students walk?
8. In set 3, if 30 bus users switch to cycles, what is the new share of cycle users?

Answers

1. 25%. Totals 120 → 150: 30/120 × 100.
2. Model B (60%). A: 20/40 = 50%. B: 15/25 = 60%. C: 15/35 ≈ 42.9%.
3. 37.5%. 45/120 = 3/8.
4. About 38.9%. (50 − 36)/36 × 100 = 14/36 × 100 ≈ 38.9%. The base is Model B.
5. 30%. 30/100 × 100.
6. About 85.7%. (130 − 70)/70 × 100 = 60/70 × 100 ≈ 85.7%.
7. 72°; 240 students. 20 × 3.6 = 72°; 20% of 1,200 = 240.
8. 17.5%. Cycle users were 15% of 1,200 = 180; now 210. 210/1,200 × 100 = 17.5%.

What to do next

• Learn the fraction–percentage table until you can recall it without thinking.
• Solve one DI set a day for two weeks, timing each set.
• After each set, note whether any mistake was a reading error or a calculation error; they need different fixes.
• In every mock, check how long DI took compared with the rest of the section.

For the arithmetic underneath DI, see percentages for SSC and fast calculation. Mean, median and the statistics questions that sometimes sit next to DI are in statistics and probability.