Logical Reasoning and Quantitative Aptitude
What you must master
Two strands appear. Logical reasoning: syllogisms and validity, contraposition, negation of quantified statements (todo, algum, nenhum), ordering/sequencing puzzles, and truth-tables for e, ou, se… então. Quantitative aptitude: percentages and percentage change, ratios and proportions, rule of three (simple and compound), averages, simple interest, and basic interpretation of tables.
Traps that appear
- Negation of “todo A é B” is “algum A não é B” - not “nenhum A é B”.
- Converse error: from “se chove, a rua molha” you may infer the contrapositive “se a rua não molha, não chove”, but NOT “se a rua molha, chove”.
- Percentage of a percentage: a 20% rise then a 20% fall does not return to the start (0.8 × 1.2 = 0.96, a 4% net loss).
- Compound rule of three: invert only inversely proportional quantities.
- Average vs. median confusion in table questions.
Rule of thumb (worked example)
For validity, ask: can I build a scenario where the premises are true and the conclusion false? If yes, the argument is invalid. Example: All auditors are careful. Some careful people are punctual. Therefore some auditors are punctual. Counter-scenario: the punctual careful people are all non-auditors - premises true, conclusion false, so invalid. For percentages, always convert to a multiplier: aumento de 15% → ×1.15; desconto de 15% → ×0.85.