Public Enterprise Korean Language Logic Ch5. The Final Weapon — Conquering High-Difficulty Quizzes and Your Roadmap to Passing

Chapter 5. The Final Weapon: Conquering High-Difficulty Quizzes

Congratulations. You’ve now made your way through everything from the basics of logic to the advanced technique of reductio ad absurdum. In this final lesson, we’ll hand you the master algorithm for staying calm and performing like an expert the moment you run into one of the “compound inference puzzles” that make test-takers cry on the real NCS or PSAT.

1. The top 1%‘s “problem-solving algorithm”

The instant you read a question, you need to decide the following four steps within five seconds.

The logic-quiz-breaking process

1. Symbolize

Reduce every sentence to →, ∧, and ∨.

2. Search for a confirmed fact

Look for information with a fixed truth value, like ~A or B.

3. Chain it together

If you have a confirmed fact, extend the chain from it. If not, take contrapositives and link things up that way.

4. Pick a strategy

If the chain breaks, push through with 'reductio ad absurdum' or 'case splitting.'

2. Evolving problem practice (Step 9: the ultimate compound-inference boss)

Question 6 (NCS/PSAT style): Given that all five of the following conditions are true, which conclusion must be true?

If A attends the meeting, B attends too.

Either B does not attend, or C attends.

If C does not attend, D attends.

If E attends, D does not attend.

A attended the meeting.

D attended and B did not attend.
Both B and C attended.
C attended and D did not attend.
A did not attend.

[A master’s thought process]

Symbolize:
- (1) A → B
- (2) ~B ∨ C (converted: B → C)
- (3) ~C → D
- (4) E → ~D (contrapositive: D → ~E)
- (5) A (confirmed information!)
Chain it together:
- Start from the confirmed fact (5): A(T).
- By (1), A → B, so → B(T).
- By the converted form of (2), B → C, so → C(T).
Can the remaining propositions be pinned down?
- Since C is true, the antecedent (~C) of (3) “~C → D” is false → whether D attends is unknown (a false antecedent forces nothing in a conditional).
- Since D is undetermined, (4) leaves whether E attends unknown as well.
- In other words, the only thing that’s 100% certain here is that A, B, and C all attended.
Check each option:
- ① Makes a claim about D and B → D is unknown, and B did attend anyway, so this is false.
- ② Both B and C attended → confirmed above. True!
- ③ Includes a claim about D → since D is unknown, this can’t be confirmed.
- ④ A did not attend → directly contradicts (5) → false.

Answer: ② Both B and C attended. (the one conclusion the chain of confirmed information forces)

3. Your final checklist before passing: “mistake prevention”

Handling “or (∨)”: Did you convert it into a conditional — “If not A, then B” — before slotting it into the chain?
“Only if ~”: Did you accidentally write the arrow backward? (A iff B)
“Some” vs. “All”: In a “Some” proposition, did you carelessly extend an arrow chain where you shouldn’t have?
Time management: If you can’t see the chain within a minute, did you immediately switch to reductio ad absurdum (making an assumption)?

🎓 A master’s final message: completing the premium-course roadmap

Studying logic is about “quality over quantity.” Rather than grinding through 100 problems on autopilot, it’s far more valuable to practice fully breaking down 10 problems into the steps of “symbolize → chain → confirm → infer.”

The reductio ad absurdum and case splitting techniques you’ve learned in this course will be powerful tools that sharpen your thinking even in complex, real-life decisions.

We’re rooting for your success!

[Appendix: a premium logic-summary PDF guide is coming soon] (This course was optimized for practical, exam-ready application.)