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        riddles >> hard >> Palindrome dates
        
(Message started by: Summer on Jul 23^rd, 2002, 11:15pm)

Title: Palindrome dates
Post by Summer on Jul 23^rd, 2002, 11:15pm

On the palindrome dates one...

The answer I got was 12/31/1321.

01 means that you have to have a month 10, so there are no other palindrome days in October, 2001. 2000 is right out, because you can't have 00 as a month. 1999 won't do either. etc.
So now we're starting to look at the century. In that case, we can settle in the year ending in 21, since the last month of a year is December. December puts us closest to 10/02/2001. If we're not going to find a palindrome day in the same year, the next closest day will be in december. the ending of the year corresponds with the month. it has no other critical role, so it can be of our choosing without restricting the results.

Thus, we've got 12/AB/BA21 so far.

So now. What's going to be the most recent century?

B has to be less than 2. That leaves 1.

So now we have 12/A1/1A21
What's the largest number A can be in a calendar year?
It's 3. 31 is the largest day number on a calendar.

So our answer is 12/31/1321.

incidently, my birthday is 09/09. A while back, when we still wrote dates X/X/XX, I got to celebrate 9/9/99.

Title: Re: Palindrome dates
Post by Xactoguy on Jul 24^th, 2002, 12:25am

There is one slight problem with your logic... All dates are written MM/DD/YYYY... even if the month has a 0 at the beginning. Therefore, although it certainly is going to be in the 1300s, the year should be 1390, giving us an answer of 09/31/1390.

And about all I get to claim is that I was born on 2/22. Too bad I won't live for another 220 years so that I can celebrate my birthday on 2/22/2222. Oh well.

Title: Re: Palindrome dates
Post by Rhaokarr on Jul 26^th, 2002, 10:04pm

And outside the US, dates are usually written in ascending or descending order (dd/mm/yyyy or yyyy/mm/dd), which alters the problem a little. Being palindromic, the date that suits one of these will naturally suit the other.

The latest non-modern date that I've come up with is 29-11-1192.

Title: Re: Palindrome dates
Post by johnP on Jul 29^th, 2002, 2:28am

Xactoguy almost got the solution right. I landed on that one as well, but there is one simple fact not taken into account: September only has 30 days, so the solution is 08/31/1380 with the mm/dd/yyyy formatting used in the US. At least I hope so! I think it is. Here in Norway we use dd/mm/yyyy, in that case the most recent date would be 29/11/1192, as already solved by Rhaokarr :)