The Grey Labyrinth is a collection of puzzles, riddles, mind games, paradoxes and other intellectually challenging diversions. Related topics: puzzle games, logic puzzles, lateral thinking puzzles, philosophy, mind benders, brain teasers, word problems, conundrums, 3d puzzles, spatial reasoning, intelligence tests, mathematical diversions, paradoxes, physics problems, reasoning, math, science.

mikegoo · Daedalian Member

When my son was little he kept saying "sumday" instead of sunday... my little brain decided there really should be a sumday and came up with a definition. sumday: any day whose day and month numbers sum to the last 2 digits of the year. February 10th was the most recent sum day 2/10/12... 2+10 = 12. This of course had my little brain thinking of all sorts of questions...

How many sumdays are/were there in 2012?

How many sumdays will there be in the next century (2101-2200)?

Trojan Horse · Daedalian Member

Got it.

There will be 11 sumdays this year: 1/11, 2/10, 3/9, etc. up to 11/1.

For the other question, each day of the year will be a sumday in exactly one year during the century. For instance, January 14 will be a sumday only in '15, March 27 will be a sumday only in '30, October 31 will only be a sumday in '41, and so on. (February 29 will never be a sumday, since '31 is not a leap year.) So there will be 365 sumdays during the century.

Thok* · Guest

As a supplement to Trojan's answer, leap day can never be a sum day, since 2+29=31 isn't a multiple of 4.

Suspence · Daedalian Member

As a side-note to this thread, I sorta have a sumlife.

Recently, I told two different people the following true story:

I can always tell how old I am just by looking at the year. All I do is take the first two digits of the year, add that to the last two digits of the year, and voila, that is my age. The best news is that it works every day of the year, except for one.

I asked both people to guess what day that is, both guessed Leap Day. Not sure what either of them were thinking, but found it odd that they both made the same very illogical guess. I suppose it helped (or hurt, from their perspective) that we were in the February of a leap year.
_________________
I hate people who try to write interesting things in their signature.

MNOWAX · 0.999... of a Troll

because you were born on Jan 2nd, 1980?
_________________
The Man The Myth The Legend
MNOWAX

L'lanmal · Daedalian Member

With two people, they should have been able to cover both possibilities. But see also the "what gender is secretariat" question.

Did anything particularly anachronistic happen to you at the end of 1999?

referee · June 21st, 2004 Member

I get two different answers: Jan 1st OR Dec 31st
_________________
Jan 21st, 2008: The pillaging continues.
Mar 4th, 2008: Rest in Peace, Gary Gygax. May your dice always roll a natural 20 wherever you are.

Be the Ultimate Ninja! Play Billy Vs. SNAKEMAN today!

Suspence · Daedalian Member

Wouldn't that be Dec 30 or Jan 2? I sure hope so, or else my story is wrong.
_________________
I hate people who try to write interesting things in their signature.

referee · June 21st, 2004 Member

Not the way you asked it (in what day it doesn't work).
_________________
Jan 21st, 2008: The pillaging continues.
Mar 4th, 2008: Rest in Peace, Gary Gygax. May your dice always roll a natural 20 wherever you are.

Be the Ultimate Ninja! Play Billy Vs. SNAKEMAN today!

Suspence · Daedalian Member

Gotcha. I believe I asked them the way I've listed it above, but might have asked which day I was born.

Either way, Leap Day is a particularly bad answer for two people (admittedly, neither are MENSA or GL members) to both arrive at separately.
_________________
I hate people who try to write interesting things in their signature.

referee · June 21st, 2004 Member

To that I agree. Interesting that they got the same clearly wrong answer independently.
_________________
Jan 21st, 2008: The pillaging continues.
Mar 4th, 2008: Rest in Peace, Gary Gygax. May your dice always roll a natural 20 wherever you are.

Be the Ultimate Ninja! Play Billy Vs. SNAKEMAN today!

Suspence · Daedalian Member

I'm reading Thinking Fast and Slow currently. It seems like the two people I asked took the path of cognitive ease...rather than taking the time to think about the math, they changed the question to "what day do I know of that is an odd day" and immediately came back with Leap Day.
_________________
I hate people who try to write interesting things in their signature.

Zag · Unintentionally offensive old coot

Most people think that free association is thinking. This destructive condition is related, I suspect, to most people not having a filter when told something by an authority figure. I firmly believe that this dangerous lack comes from having parents who didn't tease enough. I have a favorite story which explains why I teased my kids unmercifully (besides the simple fact that I enjoyed it). Extreme Delectation

When my son, whom you know here as Zahariel, was 6 or 7, he had a school friend over on a Saturday afternoon. The two of them came to me and asked (I'm not sure why they were wondering this) how far the Earth was from the Sun. Without missing a beat, I said "about five thousand miles."

Zahariel's friend just nodded and started to walk away, grateful for the information. My son, though, screwed up his face for a second and said "Wa-a-a-a-ait a minute. The United States is more than 3000 miles across, so the Earth must be a more than 5000. I know that the Sun is WAY bigger than the Earth, and you're saying that it's only that far away? It would fill up the whole sky."

I was so proud. The moral of the story is to tease your kids whenever possible. It's fun AND it's good for them. Enthusiastic Grin