A publisher named George printed monthly calendars to give away to his customers, but he soon grew tired of changing all the dates around for each subsequent month. So he designed a basic calendar body that displayed nothing but the days of the week and the date numbers. It looked like this:
“Great,” George thought. “Now I just have to make a printing plate for each possible month. When it’s time to print the next month’s calendar, I’ll simply grab the necessary plate, add the month name and year at the top, and I’ll be done.” Unfortunately, this plate-making job proved more daunting than he anticipated.
How many different plates
did George have to make?
And why?
HERE is the answer.
Comments (8)
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is it 28? 7 for the months with 31 days, 7 for those with 30, 7 for february and another 7 for a leap year. that way you have a plate for when the 1st lands on any day of the week.
posted by grant on 8-19-2008 at 7:31 am
I have an even tougher question. This came up while I was arguing about what days we would get off from our jobs for Thanksgiving. One of my coworkers said that his birthday is on Thanksgiving every four years. This sounded a little bit fishty so I went through the process of figuring out just what days could possibly have Thanksgiving happen on them. I found that he just had run into a bit of luck lately with leap years (and the non-leap year of 2000). So here’s my question: What days in November can Thanksgiving occur upon? For and even trickier task, what is my co-workers birthday?
posted by Gary on 8-19-2008 at 8:19 am
This seems wrong though. Since George would be using plates, would it not be simpler to just create the 7 plates for 31 days and then add the ink appropriately for days with 30/29/28 days so in the end he only really needs 7 plates and a knowledgeable use of ink.
Or am I thinking to hard?
posted by Aram Dermenjian on 8-19-2008 at 8:58 am
Gary: In the US, Thanksgiving is celebrated on the fourth Thursday of November, so the possible dates are Nov 22-28.
Was your friend’s birthday on the 23rd?
posted by TomH on 8-19-2008 at 9:01 am
Good thought, Aram, and I considered that notion — that he could “block” unused dates for months with fewer than 31 days. That’s why I phrased his thought to say that he’d simply add the month & year and “be done.” If he had to mess with the ink on certain months, it would require additional work for several months each year.
In the same vein, though, if he offered yearly calendars instead of monthly ones, he’d only need 14 plates (7 regular, 7 leap year) instead of 28.
posted by Sandy on 8-19-2008 at 9:06 am
Gary — 2000 was a leap year. Leap years occur every 4 years except years ending in “00″ not divisible by 400. So 1700, 1800, and 1900 were not leap years, but 1600 and 2000 were.
Bit of trivia: 1900 was the only non-leap-year in which the modern Olympics were held
posted by Kevin H on 8-19-2008 at 1:11 pm
My nephew was born on 11/27/03, which was Thanksgiving. (And yes, we called him “Butterball.”) His next birthday, the big 0-5, is on Thanksgiving again. So, it does repeat, although not exactly every four years.
posted by Cassie on 8-19-2008 at 4:30 pm
The pattern for dates falling on the same day of the week, such as a person whose birthday sometimes falls on Thanksgiving Thursday, is 5-6-11-6, every 28 years. This pattern holds from 1901 to 2099, and then will be disrupted by the year 2100 which is not a leap year. Reason for the 5-6-11-6 pattern is leap year – if you cross over 1 leap year, it’s 6 years. If you cross over 2 leap years, you only need 5 years. And the 11 is caused when leap year causes you to go from adding 6 days to 8 days, and you don’t hit adding 7 days exactly. Then you keep going until you add 14 days, in 8 normal years plus 3 leap years, for 11 total years.
posted by Richard on 11-20-2011 at 8:27 pm