Data Interpretation: Bases, Shares and Growth Rates
What it tests
Data Interpretation presents a table, bar chart, line graph, pie chart, or short caselet, then asks for comparisons, percentages, averages, growth rates, and ratios. The arithmetic is easy; marks are lost by reading the wrong row, mismatching units, or dividing before choosing the shortcut.
Rules that hold up
- Identify the base before computing any percentage: share of the total, share of a row, or growth over the previous period. The answer changes entirely.
- Growth = (new − old)/old × 100. Percentage points and per cent are different quantities when comparing two rates.
- Pie charts: a sector is a share of 360°, so its value = (angle/360) × total. When a pie is combined with another graph, check whether both pies represent the same total.
- Group averages cannot be averaged again without weighting by group size.
- Ratio questions: cancel units first. A move from 300 to 400 is a 4:3 ratio, not a 3% or 4% change.
- Approximate deliberately. Options are usually far apart, so round to one significant figure and confirm the answer band.
Worked example
A company's revenue was 240 crore in 2022 and 300 crore in 2023. Its 2023 profit margin was 12%. Find the revenue growth and the 2023 profit.
Growth = (300 − 240)/240 = 60/240 = 25%, dividing by the base year 2022, not by 300. Profit = 12% of 300 = 36 crore, applied to the year the margin belongs to. A tempting error is computing 36 as a share of the 60 crore increase.
Traps that cost marks
- Swapping row labels and column labels in a dense table.
- Reading pie-chart angles as absolute values rather than shares.
- Dividing by the new year instead of the base year for growth.
- Averaging percentages across groups of unequal size.
- Carrying full precision through every step instead of rounding at the end.