Logical Reasoning and Data Interpretation
Logical Reasoning and Data Interpretation
This domain tests conditional reasoning, syllogisms, and the interpretation of tables and graphs. The exam rewards precise reading of quantifiers ('all,' 'some,' 'only if') and of percentage versus percentage-point changes.
Core rules
- 'Only if P, Q' means Q → P. The converse is not valid; the contrapositive (not P → not Q) is valid.
- 'P is sufficient for Q' means P → Q; 'P is necessary for Q' means Q → P.
- In data questions, distinguish a percentage change from a percentage-point change, and check the base.
- Index numbers compare to a base year; do not read an index of 120 as '120% of the previous year' unless the base is the previous year.
- For ratios, keep the denominator explicit: per capita, per household, per 1,000 population.
Worked example
A budget rises from 500 to 550 billion won. The increase is 50/500 = 10%, not 50%. If defence's share rises from 25% to 30%, that is 5 percentage points, but the relative increase in the share is 5/25 = 20%. A statement that 'defence rose 30%' is therefore ambiguous and likely wrong.
Traps
Reversing 'only if' is the most common error. Do not compare percentages with different bases. Do not treat an index change of 10 points as a 10% change unless the base is 100. In syllogisms, 'some' does not imply 'some not,' and 'all' does not imply 'only.'