Thursday, July 11, 2013

On The Internet

Sharing some things from the internet, although I'm a little slow and you probably already see them. Haha.

I like this Thai Love Song by Namewee! The song is catchy as well. Check it out!

I found this interesting math question from Winnie's instagram!

Apparently there are many different "answers" on the web but I tried deriving the logic behind the answers and in my opinion, I think 1/9/1970 is the correct one!

Let me try explaining why the answer is 1/9!

Note that the dates are all arranged in order of month.

Ben - his number is either 3, 5, 9. 12. As all the numbers are repeated, he won't be able to know what is Mr Tan's birthday.

Mark - his number is either 1, 2, 4, 5, 7, 8. All the numbers are repeated, except 2 and 7. If his number was either of these, he would have known the answer straightaway.

1. Ben says "I don't know, but I can ENSURE that Mark doesn't know too."
Meaning: Ben ENSURES that Mark does not know the answer. It means that the month he is holding is definitely not 6, not 12 because he ruled out the possibility that Mark has a unique number (2 or 7). If he had 6 or 12, he cannot ENSURE that Mark did not get a unique number.

2. Mark says "INITIALLY I don't know"
Meaning: Further supports the earlier explanation. If he had gotten 2 or 7, he would have known the answer immediately. He INITIALLY do not have the answer because the number he got was a repeat. (Either 1, 4, 5, 8)

Thus, up till now, eliminated the months 6 and 12, we are left with:
4/3, 5/3, 8/3,
1/9, 5/9.

Mark also says "But I know it now"
Meaning: After eliminating 6 and 12, the number he is holding gives him the full date. It means that his number is not a repeated number after eliminated the two months. So, date 5 is out.

We are left with 4/3, 5/3, 8/3.

Ben says "Oh, then I know it too".
Meaning: So he derived from Mark's words that his date is not a repeated one anymore, so he removed date 5 and is left with only one choice in the month he is holding.

So, answer is 1/9.

What about 4/3, and 8/3?
If Ben had gotten the month 3, their conversation would have to be longer in order for Ben to find out whether it is 4 or 8. But he has gotten a 9, thus immediately concluding the answer after eliminating Date 5.

Confusing ya? Maybe my explanation wasn't clear enough! Haha. But after digesting it, it really makes sense!

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