Data Interpretation
Data Interpretation
Five questions of Paper I rest on a table, bar chart, line graph, pie chart or a combination, and test quick arithmetic under a reading of the source.
Core rules
- Pie chart: the full circle is 360° and 100%. Value of a sector = (angle/360) × total. To convert a share into degrees, multiply by 3.6.
- Growth rate: ((new − old)/old) × 100. Always divide by the base period, not the later one.
- CAGR: (end/start)^(1/n) − 1, where n is the number of intervals, not the number of years listed.
- Ratios across two charts: never compare absolute values unless both totals are known; a 30% share of a small total can be smaller than a 20% share of a large one.
- Approximate deliberately: match the option spread; if options are far apart, round to whole numbers.
Worked example
A family's monthly expenditure is ₹1,80,000, shown in a pie chart. The education sector measures 72°. What is spent on education, and what angle would it occupy if that spending rose by 25% while the total stayed unchanged?
Education = (72/360) × 1,80,000 = ₹36,000. A 25% rise gives ₹45,000. The new angle = (45,000/1,80,000) × 360 = 90°. Shortcut: since the total is fixed, the angle also rises by 25%, and 72 × 1.25 = 90°.
Traps that cost marks
- Dividing by the new value instead of the base when computing growth.
- Reading a line graph's axes as starting at zero when they are truncated, exaggerating the slope.
- Confusing "percentage of total" with "percentage more than the previous year".
- Forgetting that percentages across two different pie charts are not directly comparable.