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Old 21st February 2013, 01:35 PM   #1 (permalink)
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[LOGIC] Birthdays

I saw this on facebook, so I felt like sharing.



For reference purpose, this are my solutions. Feel free to discuss about this.

Statement 1: Ben do not know the date.
This imply that there are multiple choices for his value of M.

Statement 2: Ben ensures that Mark do not know it either.
This imply that Mark also have multiple choices for his value of N.

Statement 3: After the 2 statements, Mark knows the answer

Mark knows:
The value of N.
The value for M have multiple choices.
The date 7/6 and 2/12 are not the date. Thus the M cannot be 6 or 12. N cannot be 7 or 2.
As Mark already knows the date, it meant that through this elimination, Mark is able to pin-point to 1 date.
Thus, N= 1,4 or 8 looking at the date.

Statement 4: Ben now knows the answer:

Consider the 2 cases:
Case 1: M = 3.
Mark knows N = 4 or 8
Ben knows M = 3. But there is no way to make a judgement of what is N for Ben, as Thus this case is incorrect.

Case 2: N=1, M=9
Mark knows N=1.
Ben knows M=9, and there is only 1 possible date.

Thus, the only date that complies to this conversation is 1/9/1970

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Old 21st February 2013, 08:12 PM   #2 (permalink)
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Re: [LOGIC] Birthdays

Understood after reading solutions. But this is definitely not a PSLE question, it doesn't involve any form of math but just critical thinking instead.

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Old 21st February 2013, 08:26 PM   #3 (permalink)
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Re: [LOGIC] Birthdays

CHIM!!

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Old 21st February 2013, 10:10 PM   #4 (permalink)
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Re: [LOGIC] Birthdays

Originally Posted by MochiX View Post
Understood after reading solutions. But this is definitely not a PSLE question, it doesn't involve any form of math but just critical thinking instead.
Agreed. Definitely not a PSLE question, as it test more of logic. Just felt like sharing this over here.

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