Data Interpretation and Logical Reasoning
Data Interpretation and Logical Reasoning
This section tests speed and precision: reading tables, bar charts, line graphs and pie charts, then reasoning through arrangements, syllogisms, series and coding puzzles. The arithmetic is rarely hard; the difficulty is choosing the right base and refusing to over-infer.
Core rules
- Percentage change: (new − old) ÷ old × 100. The base is always the earlier or the stated reference value.
- Percent versus percentage points: a move from 25% to 30% is 5 percentage points but a 20% relative increase.
- Weighted averages: combine groups by their sizes, not by averaging the averages.
- Charts: pie slices total 360° and 100%; each degree is 1/360 of the total. In line graphs, check axis scales before judging a trend.
- Syllogisms: accept only conclusions that must be true in every valid diagram. Use Venn diagrams rather than intuition.
- Arrangements: fix one person or seat as a reference, then place the rest relative to it.
Worked example
Sales rose from 240 to 300 while costs rose from 180 to 210. Did the profit margin improve?
Old profit = 240 − 180 = 60, margin = 60 ÷ 240 = 25%. New profit = 300 − 210 = 90, margin = 90 ÷ 300 = 30%. The margin improved by 5 percentage points, not 5%. Note that profit itself rose by 50% (30 ÷ 60), a different and often-requested figure.
Traps
Dividing by the new value instead of the old; mixing lakh and crore; answering 5% when the question asks for percentage points; accepting a syllogism conclusion that is merely possible; and assuming a chart is drawn to scale.