Questions tagged [calendar-computations]

This tag is for questions about combinatorial and computational issues with regards to calendar systems. A typical, well-known mathematical result in this direction is John Conway's Doomsday Algorithm for computing the "day of the week" associated to a given date.

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84 views

“New Year falls more often on Sundays than on Mondays”

This is a question from a hungarian math contest from the year 1948. It was Saturday on the 23rd October, 1948. Can one conclude that New Year falls more often on Sundays than on Mondays? Well, I ...
2
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1answer
96 views

Number of occurrences of a generic recurring event between two dates

Intro Cron is a very common tool in computer science, which allows to schedule an event given a generic pattern written in a file called crontab. I'm researching on an algorithm to calculate the ...
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2answers
226 views

How to calculate my age from date of birth [closed]

I was born at 18.03.2000, Saturday 7.30pm. From year 2000 to 2001 I was $0 $ age I can not calculate my age from 2001 I will be 1 year old 2001 to 2018 subtract I had get 17 years. Please say what is ...
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4answers
1k views

Why don't we subtract out / ignore the leap year every 128 years? [closed]

When we add the extra day to the calendar every 4 years it's to "correct" the calendar under the assumption that the year's length is 365.25 days. Every year, you're .25 days off, so after 4 years, ...
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0answers
49 views

I want to know what not integer numbers means in calendar?

I want to know what not integer numbers means in this case? if $30$ days $= 4$ weeks and $2$ days $4.2$ then why $20$ days does not correspond to $2$ weeks and $8$days $4,8$? being that: $\frac{30}{...
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4answers
130 views

Identical Gregorian calendars

I ask for help. I would like to resolve the following question: Let $A$ be the set of natural numbers greater than 1582. If, for every $Y\in A$ , the years $Y$ and $Y + n$ (of the actual calendar, ...
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1answer
317 views

Difference between two dates in math formula

Good evening guys, I have little problem, I have to calculate how many days do I have between two dates which contains specific day, month and even year, do you guys have any idea how should I do that?...
2
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2answers
51 views

How can I find the day of the week which an event happened after some time has elapsed?

The problem is as follows: An astronomer discovers a new comet while scouting the skies on Monday but decides to report his discovery $256$ days after. What day of the week did the astronomer ...
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1answer
250 views

Math behind leap year cycle

Everybody knows that leap year is year which is divisible by 4. In case of century years, it has to be divisible by 400. The leap year cycle has 400 years (calendar repeat with the same day-date ...
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1answer
71 views

Tonalpohualli calculations

I was doing some math on the Tonalpohualli, the mexica ritual calendar. This calendar has 260 days divided in 13-days periods associated with 20 distinct symbols. Every 13-days period is called a ...
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1answer
53 views

Formula to find the date given a specific year, month, and day of the week

I need a formula to get me to the first or third specified day of the week of the following year. So, here is the information I am presented. I have a year (y), a month (m) and a day of the week (n). ...
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2answers
73 views

Identical calendars

We can see, for example, that the years 2009 and 2015 have identical calendars. Similarly, 2000 and 2028. I read once that given any year X at most 28 years later there will be another year Y, with ...
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0answers
144 views

Calculating which day of the week a date falls on using Gauss's algorithm and modulo arithmetic

I've been told there's a straightforward way to determine which day of the week a date falls on, by first using Gauss's algorithm, to find the day of the week of 1st of January. Then this can be ...
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2answers
84 views

I am a twin who celebrated my 13th birthday on Friday the 13th. Is this rare? What is the probability of this occurring?

I was born a twin who celebrated my 13th birthday on Friday the 13th many years ago. Is this rare? What is the probability of this occurring? I am a senior who finally wants to know the answer. ...
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2answers
30 views

How do you figure out what # of 4 a Week # is?

If we round down the number of weeks in a year to 52, And we label each of the 52 weeks either 1, 2, 3, or 4 And we label them in order, the first week of the year being 1, the second being 2, third ...
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0answers
39 views

Question based on calendars(number theory)

Number of Tuesdays in five consecutive calendar years taken together is exactly 260. Which day of the week was 1st January of the first of these five years? I don't know at all how to do this ...
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1answer
76 views

Finding the initial day of the week (Calendars)

Number of Tuesdays in five consecutive calendar years taken together is exactly $260$. Which day of the week was $1st$ January of the first of these five years? On the basis of given information the ...
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1answer
59 views

Mathematical measure of whether something's on schedule or not?

Say I decide to jog everyday for 1 km. I start jogging and I keep a log of which days I'm jogging on. Now after a couple of months, I notice in my logbook that although I jogged for 1 km on most days, ...
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2answers
3k views

Monday falls on 20th March, 1995. What was the day on 3rd November, 1994?

Monday falls on 20th March, 1995. What was the day on 3rd November, 1994? Days in November 1994( starting from 3rd)= $27$ Days in December 1994=$31$ Days in January 1995=$31$ Days in February 1995= $...
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4answers
96 views

If I wanted to determine today's date based on my birthdate, how could I do that mathematically?

Let's say for example my birthday is August 17, 1996. Each year has 365 days except leap years. If I didn't know whether 1996 was a leap year or not, is there a way I can see how many days I've been ...
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0answers
29 views

Number of 1st Jan Sundays between year a and b.

Given two year number a and b (eg a=1000 b=2000). Find the number of 1st January Sundays? Given 1st Jan 2001 was Monday? I figured that day sequence repeat after 28 years. But produced wrong answer. ...
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1answer
46 views

Finding the day of the same date of previous month?

I wanted to know if there was a short way that I could determine the day which would have been for a given date. For example, looking at the date today 4/3/17. Is there anyway we can easily ...
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1answer
31 views

Determine the busiest day from a list of dates.

There are N date ranges which include check-in date and check-out date. How can I find out the busiest day? Example: ...
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1answer
192 views

Mean number of days in a Gregorian month

Across the Gregorian calendar, what's the arithmetic mean of the number of days in each month? The context for this question is that I have some survey data in which people were asked how many times ...
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1answer
71 views

Regarding Days and Week in Calendar [closed]

How to find the Particular day for 27 -1-1932, can anyone solve the Problem, how to study the Day for particular calendar events
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4answers
777 views

Smallest future date which involves no repetition of a digit in the format DD/MM/YYYY [closed]

What is the smallest future date which involves no repetition of a digit in the format DD/MM/YYYY for the year? What is your approach?
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4answers
303 views

Why isn't 1900 a leap year? [closed]

I searched leap years online and found that 1900 is not, contrary to what I thought, a leap year. But, why is it not if 1900 is divisible by 4: $\frac{1900}{4} = 475$ My brother was working on his ...
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0answers
44 views

How can one manually calculate the date conversion to the Hebrew calendar

There already are algorithms that can be used to concert a date from different calendars into the Julian Day Number (JDN) and a JDN into the Hebrew calendar. But how can one calculate the conversion ...
3
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6answers
7k views

Can there be a month with 6 Mondays? (or 6 of any other days?)

This year, this month (November) we've 5 Mondays so I get 5 pay checks on 2nd, 9th, 15th, 22nd, 29th (which feels very good - I get paid one extra check :-). I wonder if it's possible some years to ...
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2answers
132 views

Is it possible to have such date and day combination that doesn't occur on any year ever?

My friend told me a story yesterday and said "It happened on March 13th and it was Friday". I was thinking about this and I've a question. Is it possible to have such date and day combination that it ...
0
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1answer
79 views

perpetual calendar on five dice

Does anyone know how to create a perpetual calendar on the sides of five dice ? The calendar is required to show just two digit day, and three letter month name. Apparently this can be done using ...
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1answer
45 views

how to determine particular months with five weekends

January of 2016 has five Fridays, five Saturdays and five Sundays. What is the next January that will again have five weekends like this?
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0answers
502 views

Months and notes. Pure coincidence? [closed]

There are $12$ months in a year and $12$ notes in the chromatic scale. Moreover, there are $7$ long and $5$ short months and there are $7$ white and $5$ black keys in each octave on the piano ...
2
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2answers
81 views

Friday the 13th future possible

A year normally has at most three Fridays the 13th. Year 2015 has three such days. What is the next year that has three Fridays the 13th again for the first time?
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1answer
96 views

how to determine the day of the week when some clues are given?

In a year, there are more Mondays than Fridays, and more Sundays than Wednesdays. Which day of the week is the first day in March of that year?
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1answer
43 views

What adjustments would be necessary to have a remainder of 0 associated with Sunday?

I was reading this below and I had a question: http://mathforum.org/dr.math/faq/faq.calendar.html Take a look under "The Key Value Method" where it says "A remainder of 0 corresponds to Saturday, 1 ...
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1answer
118 views

Why do you subtract 1 in a leap year if the date falls before March?

I was reading this below and I had a question: http://mathforum.org/dr.math/faq/faq.calendar.html Take a look under "The Key Value Method" where it says "If your date is in January or February of a ...
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1answer
839 views

Probability that a year contains 53 Mondays

The question: Find a probability that a year chosen at random has 53 Mondays. Now I know in a non-leap year, probability of getting 53 Mondays is $\frac{1}{7}$ and in a leap year, probability of ...
2
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1answer
294 views

A question about leap year

Very difficult to me, It is a question about leap years: "In the western calendar, a year having 365 days is called a common year, while a year having 366 days (with an extra day, February 29) is ...
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0answers
147 views

About an answer given for Project Euler 19

The problem is here and someone gave this answer but I don't understand it even if I know the rule of large numbers. If you want to write a code for this, it is really boring. On the other hand, if ...
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2answers
358 views

Calculate the distance between days of the week

I'm trying to create a formula that will give me the distance in days between 2 different days of the week with min/max of +7/-7. So for instance is there a formula to find that the days between this ...
2
votes
3answers
5k views

Which day of the week will be $100$ days from now

If today is Wednesday, what day of the week will it be $100$ days from now? Going forward $1,8,15,\dots,92,99$ days all result in Wednesday. So the $100$th day will be Thursday. But the solution ...
28
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3answers
23k views

Why does this age calculation trick work?

The trick works like this: Take the current date in the format yyyymmdd and subtract it with your date of birth taken in the same format. Drop the last four digits to get your age. For example, I was ...
2
votes
4answers
227 views

probability that a number is a leap year

I have been asked the following question in an exam in Mathematics Phd Programme as a level of IQ Test. However I don't know how to figure it out. November 9,1994 was a Wednesday. Then what day will ...
7
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2answers
345 views

Under the Gregorian calendar, what days can never be Easter?

Obviously, October 31 can't be Easter any year whatsoever. Indeed no day in October can be Easter. But can February 28 be Easter? What about February 29? May 1? Is there a single consecutive range of ...
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1answer
98 views

Proof about Friday the 13th

Few years ago I learned that there are more friday the 13th in the 400 years period of our calendar, than all other days, but I have never found any proof ! Can you help me please ?
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1answer
766 views

Is Christmas equally Likely to fall on any day of the week? [duplicate]

Assuming Christmas day falls on the 25th of December every year, and using the Gregorian calendar, is it equally likely to fall on any day of the week? (With no prior knowledge about last year's ...
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3answers
465 views

Calculate difference in days to reference date

This question is related to a programming question. Because I think it's pure mathematic I post this question here. I want to calculate the difference in days to a reference point. Therefore I have ...
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0answers
637 views

Question about Gauss' Determination of the first day of the year.

On the wikipedia article http://en.wikipedia.org/wiki/Determination_of_the_day_of_the_week#Gauss.27_algorithm it explains the Gaussian Formula for calculating the first day of the year. I was ...
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1answer
3k views

Converting decimal dates to calendar dates?

I have the decimal number 2005.067 which represents the date January 25, 2005. The math equation below shows how the decimal number is created 2005 + (25 - 0.5)/365. I want to be able to grab 2005.067 ...