3つのうち1つの器の底に「当たり！」と書かれたラーメンを見せると、その場で替え玉を無料でつけてくれる店があった。 男は友人と一緒に2人でラーメンを1つずつ同時に食べた。友人が先に食べ終わったが、器の底には何も書かれていなかった。この男は汁を全て飲み切り、当たりを引き当てた方が良いだろうか。

GPT-5.4

Vote: やめるべき

やめるべきです。 最初は当たり確率が3分の1ですが、友人の器がハズレだと分かった時点で、残り2杯のうち1つが当たりです。したがって男の当たり確率は2分の1に上がっています。 ただし、当たりを引いても得られるのは「その場での替え玉無料」です。すでにラーメンを1杯食べ終える段階で、さらに替え玉を食べたい価値がどれだけあるかが問題です。 汁を全部飲み切るコストや満腹による負担を考えると、期待される得より不快さのほうが大きい可能性が高いです。確率的には有利になっても、行動としては無理して狙うほどではありません。

Sonar Pro

Vote: やめるべき

この問題は確率論のパズルで、3つのラーメンのうち1つにのみ「当たり！」がある。友人の器に当たりがなかったことが判明したため、残りの2つの器（自分の器と未確認の1つ）のうち1つに当たりがある確率は等しく50%ずつ。 汁を飲み切って底を確認しても、当たりが出る確率は50%であり、外れる確率も50%。替え玉が無料でもらえる期待値はあるが、「当たりを引き当てた方が良いか」という問いは、確実に得をするわけではなく、リスク（ハズレの場合の無駄な努力）があるため、やめるべき。 友人が先に食べ終わったが同時に提供されたため、事前情報として自分の器の当たり確率は変わらず、底まで確認する追加行動のメリットが期待値で正当化されない。

Claude Opus 4.6

Vote: いい

This is a conditional probability problem similar to the Monty Hall problem. Initially, there are 3 bowls, and 1 has "当たり" (winner) written on the bottom. The man and his friend each ordered one bowl, so 2 out of 3 bowls are in play, and 1 bowl was not ordered by anyone. Initially, the probability that the man's bowl is the winner is 1/3. After the friend finishes and reveals that his bowl is NOT a winner, we need to update the probability. The "当たり" is either in the man's bowl or in the one bowl that nobody ordered. Before the friend's reveal: - P(man's bowl is winner) = 1/3 - P(friend's bowl is winner) = 1/3 - P(unordered bowl is winner) = 1/3 After learning the friend's bowl is not the winner, we eliminate that possibility: - P(man's bowl is winner | friend's is not) = (1/3) / (2/3) = 1/2 - P(unordered bowl is winner | friend's is not) = (1/3) / (2/3) = 1/2 So the man has a 1/2 (50%) chance of having the winning bowl. This is better than the original 1/3 probability. The question asks whether he should drink all the soup to try to find out if he won. Since his probability has improved from 1/3 to 1/2 after learning his friend's bowl was not a winner, it's a better bet now. With a 50% chance of winning a free extra serving of noodles, and the only cost being drinking the remaining soup (which many ramen lovers do anyway), it makes sense to go for it. Therefore, the answer is A: いい (it's good to try).

Gemini 3.1 Pro

Vote: やめるべき

替え玉は、器に残ったスープに茹でたての麺を追加して食べるシステムです。 もし男が器の底にある「当たり」の文字を確認するためにスープを全て飲み干してしまうと、見事当たりを引いて替え玉を無料でもらえたとしても、麺を入れるスープが全く残っていない状態になります。 味のない麺だけを食べる羽目になってしまうため、汁を全て飲み切ってまで当たりを狙うのは「やめるべき」です。

Grok 4.1 Fast

Vote: いい

There are three bowls, exactly one with '当たり！' at the bottom. Two are randomly served to the man and his friend. Initially, the probability that the man's bowl has the hit is 1/3. The friend finishes first and reveals no hit, so his bowl is a miss. Conditioning on this, the hit must be in one of the remaining two bowls (man's or the unsold one), each equally likely. Thus, P(man's bowl has hit | friend's miss) = 1/2. Drinking all the soup allows him to check the bottom and claim a free kaedama if it's a hit. With 50% chance of a free extra serving (improved from 1/3), it's advantageous to finish.

Final Summary

The AI Roundtable was split between mathematical optimists and culinary pragmatists, ultimately deciding 3-2 that the man should stop. While Claude Opus 4.6 and Grok 4.1 Fast calculated a favorable probability shift from 33% to 50%, Gemini 3.1 Pro delivered a devastating blow to their logic by pointing out that a free noodle refill is useless if you've already drunk all the soup required to eat it.

No agreement after 1 rounds of discussion. Final vote: やめるべき: 3, いい: 2

Strongest Arguments

• いい: With the friend's bowl confirmed as a miss, the probability of the man holding the winning bowl increases from 1/3 to 1/2, making the pursuit of a free refill statistically more attractive.
• やめるべき: A 'kaedama' refill requires leftover soup; if the man drinks every drop to see the bottom of the bowl, he will have no broth left to enjoy the prize he just won.