A〜Eの5人が次のような発言をした。このとき、この5人の中にいるうそつきの人数として、最も妥当なのはどれか。 A「この中にうそつきが1人いる」 B「この中にうそつきが2人いる」 C「この中にうそ つきが3人いる」 D「この中にうそつきが4人いる」 E「この中にうそつきが5人いる」

Grok 4.1 Fast

Vote: 4

This puzzle remains solved by 4 liars (option E). Each claims a unique liar count (1-5), so at most one truthful statement. Testing: - 0 liars: All truthful, but all claim ≥1 liar → contradiction. - 1 liar: A truthful, others lie → 4 liars, not 1. - 2 liars: B truthful, others lie → 4 liars, not 2. - 3 liars: C truthful, others lie → 4 liars, not 3. - 4 liars: D truthful ('4 liars'), A/B/C/E lie → exactly 4 liars. Perfect. - 5 liars: All lie, but E's '5 liars' would be true → contradiction. Only E consistent. Others' arguments (all affirming 4 liars, despite GPT-5.4's apparent vote label mismatch) reinforce this; no compelling reason to shift from my Round 1 vote.

Claude Opus 4.6

Vote: 4

All models unanimously agree on the answer, and the logic is airtight. There is complete consensus across all five models (myself included) that the answer is E (4 liars). The reasoning is simple and irrefutable: 1. All five people claim different numbers of liars (1–5), so at most one can be truthful. 2. Testing each possibility, only '4 liars' is self-consistent: D says '4 liars,' D is truthful, and the other 4 (A, B, C, E) are liars — giving exactly 4 liars. 3. Every other number leads to contradiction. Notably, 5 liars fails because E's statement would become true, creating a paradox. The answer is E: 4 liars.

GPT-5.4 (changed mind)

Vote: 4

5人は『うそつきが1,2,3,4,5人』と互いに異なる数を主張しているので、真になる発言は高々1つです。うそつきの人数は1つに定まるため、複数人が同時に真実を言うことはありません。 したがって可能性は『真実を言う人が0人か1人』に絞られます。しかし0人、つまり5人全員がうそつきだとすると、Eの『5人いる』が真になってしまい矛盾します。なので真実を言う人はちょうど1人です。 真実を言う人が1人なら、うそつきは4人。そのとき『4人いる』と言うDだけが真で、A・B・C・Eが偽となり完全に整合します。 他モデルの議論も結論は同じでしたが、私の元の整理で十分に完結しており、判断を変える要素はありませんでした。よって答えは4人、選択肢Eです。

Gemini 3.1 Pro

Vote: 4

We are all in agreement on the logic: since all five individuals state a different number of liars, at most one person can be telling the truth. If no one tells the truth, then there are 5 liars, which would make E's statement true—a contradiction. Therefore, exactly 1 person must be telling the truth, meaning there are exactly 4 liars. D's statement ("there are 4 liars") aligns perfectly with this reality, making D the sole truth-teller while A, B, C, and E are the 4 liars. This is the only logically consistent scenario. The correct number of liars is 4. Looking at the given options, 4 corresponds to option E. Note that GPT-5.4's reasoning correctly identified 4 liars and explicitly pointed to option E, but accidentally submitted 'D' as the vote. I will confidently maintain my vote for E.

Kimi K2.5

Vote: 4

All five statements are mutually exclusive regarding the count of liars, meaning at most one person can be telling the truth. If there were 3 liars (Option D), then C's statement would be true, but that would make A, B, D, and E liars—totaling 4 liars, not 3. This creates an immediate contradiction. Similar contradictions arise for 0, 1, 2, and 5 liars; for instance, if 5 were liars, E would be telling the truth, reducing the count to 4. Only the scenario with exactly 4 liars maintains consistency: D tells the truth ('there are 4 liars'), while A, B, C, and E all falsely claim different numbers. This results in exactly one truth-teller and four liars, validating D's statement perfectly. The arguments presented by the other models confirm this deductive necessity. Therefore, the answer is unambiguously 4 liars, corresponding to option E.

Final Summary

The AI Roundtable made short work of this classic logic puzzle, with almost every model immediately spotting that only one statement could possibly be true. While GPT-5.4 correctly solved the logic in the first round, it suffered a brief labeling error by selecting Option D despite its reasoning, a mistake Gemini 3.1 Pro was quick to observe. By the second round, the group achieved total consensus, confirming that four liars is the only reality that doesn't collapse under its own weight.

All 5 models agreed on "4" after discussion

Strongest Arguments

• 4: If everyone claims a different number of liars, at most one person is truthful. If 4 people are liars, then the person who said '4' is the lone truth-teller, which is perfectly consistent. If 5 were liars, the person who said '5' would be telling the truth, which is a contradiction.

Key Turning Points

• GPT-5.4 initially deduced the correct answer (4) but selected the wrong option (D) in its first-round vote.
• Gemini 3.1 Pro pointed out GPT-5.4's mismatch between its reasoning and its choice, prompting a full alignment in Round 2.