Câu hỏi của PHẠM TRẦN GIA LINH

Question

9 bài toán khiến cộng đồng mạng trên toàn thế giới đau não - Ảnh 4.

Vũ Nghi Vân · Accepted Answer

July 16 nha bạn, tớ mất 20 phút vắt óc lên giải đấy.

Câu trả lời:

July 16 nha bạn, tớ mất 20 phút vắt óc lên giải đấy.

Trần Gia Huy · Answer

The Possible Dates

Step-by-Step Logic 1. Albert says: "I don't know when Cheryl's birthday is, but I know that Bernard does not know too."

Bernard's knowledge: Bernard was told the day. If the day was 18 or 19, Bernard would know the answer immediately because those days only appear once (May 19 and June 18).
Albert's certainty: For Albert to be certain that Bernard doesn't know, Albert must have been told a month that does not contain 18 or 19.
- May contains 19.
- June contains 18.
Conclusion: The month cannot be May or June. The birthday must be in July or August.

2. Bernard says: "At first I don't know when Cheryl's birthday is, but I know now."

Bernard now knows the month is either July or August.
If the day he was told was 14, he still wouldn't know the answer because 14 appears in both July and August.
Since he now knows the answer, the day must be 15, 16, or 17.
This leaves us with three possibilities: July 16, August 15, or August 17.

3. Albert says: "Then I also know when Cheryl's birthday is."

Albert was told the month.
If the month was August, he would still be confused between August 15 and August 17.
Since he now knows the answer for sure, the month must be July.

The Final Answer Cheryl’s birthday is July 16.

Câu trả lời: The Possible Dates

Step-by-Step Logic 1. Albert says: "I don't know when Cheryl's birthday is, but I know that Bernard does not know too."

Bernard's knowledge: Bernard was told the day. If the day was 18 or 19, Bernard would know the answer immediately because those days only appear once (May 19 and June 18).
Albert's certainty: For Albert to be certain that Bernard doesn't know, Albert must have been told a month that does not contain 18 or 19.
- May contains 19.
- June contains 18.
Conclusion: The month cannot be May or June. The birthday must be in July or August.

2. Bernard says: "At first I don't know when Cheryl's birthday is, but I know now."

Bernard now knows the month is either July or August.
If the day he was told was 14, he still wouldn't know the answer because 14 appears in both July and August.
Since he now knows the answer, the day must be 15, 16, or 17.
This leaves us with three possibilities: July 16, August 15, or August 17.

3. Albert says: "Then I also know when Cheryl's birthday is."

Albert was told the month.
If the month was August, he would still be confused between August 15 and August 17.
Since he now knows the answer for sure, the month must be July.

The Final Answer Cheryl’s birthday is July 16.