The mother of all age-of-the-captain riddles












12












$begingroup$


A few days ago, as I was delving into the mess in my grand parents' attic, I found an impressive ancient book that was written in a language that I had never seen before.



"This book is a collection of riddles printed in the eighteenth century." Grandma said. "One in particular is worth reading: it is said to be the ancestor of the age-of-the-captain riddles. Let me translate it to you."



And she proceeded:




A Captain's son asks his father:



"Why Father, I've noticed that we never celebrate your birthday, and in fact I don't think I even know when you were born."



Answers the Captain:



"If you subtract four from the day I was born, then you get a non-zero
integer with several distinct prime divisors, one of which is the
month I was born. Now with that knowledge, if I tell you the day I
was born, then you shall know the year as well."



What was the Captain's date of birth? (dd/mm/yyyy)




She then closed the book and stared into my eyes with the most mischievous look I'd ever seen. She asked:



"In what language was this book written?"






language history arithmetic







share|improve this question







New contributor




Arnaud Mortier is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$












  • $begingroup$
    ... is it his mother? proceeds to read beyond the title
    $endgroup$
    – Riddler
    6 hours ago
















12












$begingroup$


A few days ago, as I was delving into the mess in my grand parents' attic, I found an impressive ancient book that was written in a language that I had never seen before.



"This book is a collection of riddles printed in the eighteenth century." Grandma said. "One in particular is worth reading: it is said to be the ancestor of the age-of-the-captain riddles. Let me translate it to you."



And she proceeded:




A Captain's son asks his father:



"Why Father, I've noticed that we never celebrate your birthday, and in fact I don't think I even know when you were born."



Answers the Captain:



"If you subtract four from the day I was born, then you get a non-zero
integer with several distinct prime divisors, one of which is the
month I was born. Now with that knowledge, if I tell you the day I
was born, then you shall know the year as well."



What was the Captain's date of birth? (dd/mm/yyyy)




She then closed the book and stared into my eyes with the most mischievous look I'd ever seen. She asked:



"In what language was this book written?"






language history arithmetic







share|improve this question







New contributor




Arnaud Mortier is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$












  • $begingroup$
    ... is it his mother? proceeds to read beyond the title
    $endgroup$
    – Riddler
    6 hours ago














12












12








12


2



$begingroup$


A few days ago, as I was delving into the mess in my grand parents' attic, I found an impressive ancient book that was written in a language that I had never seen before.



"This book is a collection of riddles printed in the eighteenth century." Grandma said. "One in particular is worth reading: it is said to be the ancestor of the age-of-the-captain riddles. Let me translate it to you."



And she proceeded:




A Captain's son asks his father:



"Why Father, I've noticed that we never celebrate your birthday, and in fact I don't think I even know when you were born."



Answers the Captain:



"If you subtract four from the day I was born, then you get a non-zero
integer with several distinct prime divisors, one of which is the
month I was born. Now with that knowledge, if I tell you the day I
was born, then you shall know the year as well."



What was the Captain's date of birth? (dd/mm/yyyy)




She then closed the book and stared into my eyes with the most mischievous look I'd ever seen. She asked:



"In what language was this book written?"






language history arithmetic







share|improve this question







New contributor




Arnaud Mortier is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$




A few days ago, as I was delving into the mess in my grand parents' attic, I found an impressive ancient book that was written in a language that I had never seen before.



"This book is a collection of riddles printed in the eighteenth century." Grandma said. "One in particular is worth reading: it is said to be the ancestor of the age-of-the-captain riddles. Let me translate it to you."



And she proceeded:




A Captain's son asks his father:



"Why Father, I've noticed that we never celebrate your birthday, and in fact I don't think I even know when you were born."



Answers the Captain:



"If you subtract four from the day I was born, then you get a non-zero
integer with several distinct prime divisors, one of which is the
month I was born. Now with that knowledge, if I tell you the day I
was born, then you shall know the year as well."



What was the Captain's date of birth? (dd/mm/yyyy)




She then closed the book and stared into my eyes with the most mischievous look I'd ever seen. She asked:



"In what language was this book written?"






language history arithmetic




language history arithmetic






share|improve this question







New contributor




Arnaud Mortier is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|improve this question







New contributor




Arnaud Mortier is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|improve this question




share|improve this question






New contributor




Arnaud Mortier is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









asked 7 hours ago









Arnaud MortierArnaud Mortier

1815




1815




New contributor




Arnaud Mortier is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.





New contributor





Arnaud Mortier is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






Arnaud Mortier is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












  • $begingroup$
    ... is it his mother? proceeds to read beyond the title
    $endgroup$
    – Riddler
    6 hours ago


















  • $begingroup$
    ... is it his mother? proceeds to read beyond the title
    $endgroup$
    – Riddler
    6 hours ago
















$begingroup$
... is it his mother? proceeds to read beyond the title
$endgroup$
– Riddler
6 hours ago




$begingroup$
... is it his mother? proceeds to read beyond the title
$endgroup$
– Riddler
6 hours ago










2 Answers
2






active

oldest

votes


















13












$begingroup$


First, the day, minus 4, must have at least two prime factors ("several distinct prime divisors"). Moreover, we will know his month uniquely, so one of these primes should be greater than 12 or the date greater than 28. (Checking 29 and 31 - both 29-4 and 31-4 have only one distinct prime divisor, so neither work.) So the date should be 30=2*13+4.

So his birthday is on February 30. The next larger candidate would be 2*17+4 or February 38, followed by February 42 and March 43, which are obviously not real dates.

Wait, say what?? Yes, that's a real thing! In particular, it satisfies the date requirement (we now know that his birthday was on 30/02/1712), we now know why we never celebrate his birthday (since February 30 never existed thereafter), and we also know the language it was written in, namely Swedish.







share|improve this answer











$endgroup$









  • 1




    $begingroup$
    That’s pretty neat, but one minor nitpick - pretty sure 25 is not prime (it does have only one prime divisor though so it’s still ruled out by that)
    $endgroup$
    – Jeff
    5 hours ago



















0












$begingroup$

Is the answer:




02/03/1700?


Four days before that would be 26/02/1700. The month has 2 distinct prime divisors, 2 and 13, one of which is the month.


The only part of the calendar which differs from year to year is 29/02. So the 4 day stretch must span this date, if it is true that the year can be deduced by the day.


Years divisible by 100, but not 400, do not have a leap day. Of the numbers {25, 26, 27, 28, 29}, only 26 has distinct prime divisors. And 4 days ahead of 26/02 is 02/03, in a non-leap year.


The next question is the century. But the second paragraph states that the riddles were published in the 18th century (ie., the 1700s). If the Captain was alive during the 1700s then only the year 1700 makes sense.


As for the language, that has me stumped. :)







share|improve this answer










New contributor




Andrew is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






$endgroup$









  • 1




    $begingroup$
    Welcome to Puzzling.SE! We generally hide our answers by using the spoiler tag ('>!') so that fellow puzzlers can choose whether or not to see proposed answers :)
    $endgroup$
    – Dmihawk
    2 hours ago











Your Answer





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2 Answers
2






active

oldest

votes








2 Answers
2






active

oldest

votes









active

oldest

votes






active

oldest

votes









13












$begingroup$


First, the day, minus 4, must have at least two prime factors ("several distinct prime divisors"). Moreover, we will know his month uniquely, so one of these primes should be greater than 12 or the date greater than 28. (Checking 29 and 31 - both 29-4 and 31-4 have only one distinct prime divisor, so neither work.) So the date should be 30=2*13+4.

So his birthday is on February 30. The next larger candidate would be 2*17+4 or February 38, followed by February 42 and March 43, which are obviously not real dates.

Wait, say what?? Yes, that's a real thing! In particular, it satisfies the date requirement (we now know that his birthday was on 30/02/1712), we now know why we never celebrate his birthday (since February 30 never existed thereafter), and we also know the language it was written in, namely Swedish.







share|improve this answer











$endgroup$









  • 1




    $begingroup$
    That’s pretty neat, but one minor nitpick - pretty sure 25 is not prime (it does have only one prime divisor though so it’s still ruled out by that)
    $endgroup$
    – Jeff
    5 hours ago
















13












$begingroup$


First, the day, minus 4, must have at least two prime factors ("several distinct prime divisors"). Moreover, we will know his month uniquely, so one of these primes should be greater than 12 or the date greater than 28. (Checking 29 and 31 - both 29-4 and 31-4 have only one distinct prime divisor, so neither work.) So the date should be 30=2*13+4.

So his birthday is on February 30. The next larger candidate would be 2*17+4 or February 38, followed by February 42 and March 43, which are obviously not real dates.

Wait, say what?? Yes, that's a real thing! In particular, it satisfies the date requirement (we now know that his birthday was on 30/02/1712), we now know why we never celebrate his birthday (since February 30 never existed thereafter), and we also know the language it was written in, namely Swedish.







share|improve this answer











$endgroup$









  • 1




    $begingroup$
    That’s pretty neat, but one minor nitpick - pretty sure 25 is not prime (it does have only one prime divisor though so it’s still ruled out by that)
    $endgroup$
    – Jeff
    5 hours ago














13












13








13





$begingroup$


First, the day, minus 4, must have at least two prime factors ("several distinct prime divisors"). Moreover, we will know his month uniquely, so one of these primes should be greater than 12 or the date greater than 28. (Checking 29 and 31 - both 29-4 and 31-4 have only one distinct prime divisor, so neither work.) So the date should be 30=2*13+4.

So his birthday is on February 30. The next larger candidate would be 2*17+4 or February 38, followed by February 42 and March 43, which are obviously not real dates.

Wait, say what?? Yes, that's a real thing! In particular, it satisfies the date requirement (we now know that his birthday was on 30/02/1712), we now know why we never celebrate his birthday (since February 30 never existed thereafter), and we also know the language it was written in, namely Swedish.







share|improve this answer











$endgroup$




First, the day, minus 4, must have at least two prime factors ("several distinct prime divisors"). Moreover, we will know his month uniquely, so one of these primes should be greater than 12 or the date greater than 28. (Checking 29 and 31 - both 29-4 and 31-4 have only one distinct prime divisor, so neither work.) So the date should be 30=2*13+4.

So his birthday is on February 30. The next larger candidate would be 2*17+4 or February 38, followed by February 42 and March 43, which are obviously not real dates.

Wait, say what?? Yes, that's a real thing! In particular, it satisfies the date requirement (we now know that his birthday was on 30/02/1712), we now know why we never celebrate his birthday (since February 30 never existed thereafter), and we also know the language it was written in, namely Swedish.








share|improve this answer














share|improve this answer



share|improve this answer








edited 5 hours ago

























answered 7 hours ago









phenomistphenomist

8,3223053




8,3223053








  • 1




    $begingroup$
    That’s pretty neat, but one minor nitpick - pretty sure 25 is not prime (it does have only one prime divisor though so it’s still ruled out by that)
    $endgroup$
    – Jeff
    5 hours ago














  • 1




    $begingroup$
    That’s pretty neat, but one minor nitpick - pretty sure 25 is not prime (it does have only one prime divisor though so it’s still ruled out by that)
    $endgroup$
    – Jeff
    5 hours ago








1




1




$begingroup$
That’s pretty neat, but one minor nitpick - pretty sure 25 is not prime (it does have only one prime divisor though so it’s still ruled out by that)
$endgroup$
– Jeff
5 hours ago




$begingroup$
That’s pretty neat, but one minor nitpick - pretty sure 25 is not prime (it does have only one prime divisor though so it’s still ruled out by that)
$endgroup$
– Jeff
5 hours ago











0












$begingroup$

Is the answer:




02/03/1700?


Four days before that would be 26/02/1700. The month has 2 distinct prime divisors, 2 and 13, one of which is the month.


The only part of the calendar which differs from year to year is 29/02. So the 4 day stretch must span this date, if it is true that the year can be deduced by the day.


Years divisible by 100, but not 400, do not have a leap day. Of the numbers {25, 26, 27, 28, 29}, only 26 has distinct prime divisors. And 4 days ahead of 26/02 is 02/03, in a non-leap year.


The next question is the century. But the second paragraph states that the riddles were published in the 18th century (ie., the 1700s). If the Captain was alive during the 1700s then only the year 1700 makes sense.


As for the language, that has me stumped. :)







share|improve this answer










New contributor




Andrew is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






$endgroup$









  • 1




    $begingroup$
    Welcome to Puzzling.SE! We generally hide our answers by using the spoiler tag ('>!') so that fellow puzzlers can choose whether or not to see proposed answers :)
    $endgroup$
    – Dmihawk
    2 hours ago
















0












$begingroup$

Is the answer:




02/03/1700?


Four days before that would be 26/02/1700. The month has 2 distinct prime divisors, 2 and 13, one of which is the month.


The only part of the calendar which differs from year to year is 29/02. So the 4 day stretch must span this date, if it is true that the year can be deduced by the day.


Years divisible by 100, but not 400, do not have a leap day. Of the numbers {25, 26, 27, 28, 29}, only 26 has distinct prime divisors. And 4 days ahead of 26/02 is 02/03, in a non-leap year.


The next question is the century. But the second paragraph states that the riddles were published in the 18th century (ie., the 1700s). If the Captain was alive during the 1700s then only the year 1700 makes sense.


As for the language, that has me stumped. :)







share|improve this answer










New contributor




Andrew is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






$endgroup$









  • 1




    $begingroup$
    Welcome to Puzzling.SE! We generally hide our answers by using the spoiler tag ('>!') so that fellow puzzlers can choose whether or not to see proposed answers :)
    $endgroup$
    – Dmihawk
    2 hours ago














0












0








0





$begingroup$

Is the answer:




02/03/1700?


Four days before that would be 26/02/1700. The month has 2 distinct prime divisors, 2 and 13, one of which is the month.


The only part of the calendar which differs from year to year is 29/02. So the 4 day stretch must span this date, if it is true that the year can be deduced by the day.


Years divisible by 100, but not 400, do not have a leap day. Of the numbers {25, 26, 27, 28, 29}, only 26 has distinct prime divisors. And 4 days ahead of 26/02 is 02/03, in a non-leap year.


The next question is the century. But the second paragraph states that the riddles were published in the 18th century (ie., the 1700s). If the Captain was alive during the 1700s then only the year 1700 makes sense.


As for the language, that has me stumped. :)







share|improve this answer










New contributor




Andrew is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






$endgroup$



Is the answer:




02/03/1700?


Four days before that would be 26/02/1700. The month has 2 distinct prime divisors, 2 and 13, one of which is the month.


The only part of the calendar which differs from year to year is 29/02. So the 4 day stretch must span this date, if it is true that the year can be deduced by the day.


Years divisible by 100, but not 400, do not have a leap day. Of the numbers {25, 26, 27, 28, 29}, only 26 has distinct prime divisors. And 4 days ahead of 26/02 is 02/03, in a non-leap year.


The next question is the century. But the second paragraph states that the riddles were published in the 18th century (ie., the 1700s). If the Captain was alive during the 1700s then only the year 1700 makes sense.


As for the language, that has me stumped. :)








share|improve this answer










New contributor




Andrew is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|improve this answer



share|improve this answer








edited 2 hours ago









Dmihawk

2,488728




2,488728






New contributor




Andrew is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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answered 2 hours ago









AndrewAndrew

1




1




New contributor




Andrew is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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New contributor





Andrew is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






Andrew is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.








  • 1




    $begingroup$
    Welcome to Puzzling.SE! We generally hide our answers by using the spoiler tag ('>!') so that fellow puzzlers can choose whether or not to see proposed answers :)
    $endgroup$
    – Dmihawk
    2 hours ago














  • 1




    $begingroup$
    Welcome to Puzzling.SE! We generally hide our answers by using the spoiler tag ('>!') so that fellow puzzlers can choose whether or not to see proposed answers :)
    $endgroup$
    – Dmihawk
    2 hours ago








1




1




$begingroup$
Welcome to Puzzling.SE! We generally hide our answers by using the spoiler tag ('>!') so that fellow puzzlers can choose whether or not to see proposed answers :)
$endgroup$
– Dmihawk
2 hours ago




$begingroup$
Welcome to Puzzling.SE! We generally hide our answers by using the spoiler tag ('>!') so that fellow puzzlers can choose whether or not to see proposed answers :)
$endgroup$
– Dmihawk
2 hours ago










Arnaud Mortier is a new contributor. Be nice, and check out our Code of Conduct.










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