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Browse Middle School Calendars/Dates/Time
Stars indicate particularly interesting answers or good places to begin browsing.

Selected answers to common questions:
    A million/billion seconds.
    Time zones.



Deriving Zeller's Rule [02/25/2003]
How do you derive the formula f=k+[(13*m-1)/5]+d+[d/4]+[c/4]-2*c?

One Million Seconds [09/10/2001]
What is a million seconds in weeks, days, hours, minutes, and seconds? What does unit conversion have to do with number bases?

12-Hour and 24-Hour Time [04/25/2002]
If it is 00:46 on the clock, what would the time be for 12 hour time?

24 Hours in a Day [08/15/2001]
Why divide the day into 24 equal parts? Why not 23 or 25?

Adding and Subtracting Units of Time [12/11/1998]
How do you subtract units of time? In particular, how do you borrow from hours to make the minutes bigger?

Adding Hours and Minutes [01/11/1997]
What time is it 2 hours and 55 minutes after 8:50 A.M.?

Adding Time [04/26/1999]
A spacecraft is launched at 7:45 a.m. on Monday and flies for 5 days, 3 hours, and 18 minutes. What time does it land?

Alternate Method for Adding Time [02/09/2001]
I have come up with a simpler technique for adding and subtracting time values given in hours and minutes, or minutes and seconds. Can you tell me how I can publish my method, which I call the Siri Factor?

Analog and Digital Time [11/15/2004]
What is 4:05 in analog time?

Averaging Minutes and Seconds [07/03/2002]
I need the average time of 20 different times. If I enter, say, 4 minutes and 25 seconds as 4.25, I come up with the wrong average. How should I do it?

A Billion Seconds [10/21/1996]
If I was born on 01/02/84, when will I have been alive for a billion seconds?

Birthdays Every Year [05/14/1999]
Why does my birthday day of the week always go up each year?

Calculating Average Starting Time [06/23/2003]
How do you average a series of starting times to get the average starting time? Say 9:30a.m., 10:15a.m., 11:45a.m., 1:30p.m., and 11:30a.m.

Calculating How Many Days between Two Dates [10/06/2004]
I'm trying to figure out how may days it will be before we reach July 10, 2006, and I can't figure out how to go about it other than taking a calendar and counting by hand. Is there a way to calculate it?

Calculating Timecards [08/03/1999]
Is there a formula to find how many hours a person worked?

Calendar Repeats [05/06/2002]
What is the next year after 1991 with the same calendar as 1990?

Changing Time Zones [11/17/1999]
If an airplane leaves New York at 09:15 to travel to London, and the flight takes 5 hrs. 45 min., what will the local time be when the plane lands?

China's Time Zone [12/01/2000]
Why does the former USSR have 11 time zones, while China has only 1?

Clock Hands and Hours Worked [01/29/2003]
A man arrives at work between 8:00 and 9:00 a.m. at exactly the moment the minute hand and hour hand of the clock point in the same direction.... How many hours did the man work?

Conversion of Time Range into Minutes [11/13/2002]
What equation/conversion can I use to find the number of minutes between the start and end times for both 'available' and 'actual' time on a 24-hour clock?

Converting Gregorian Date to Gregorian Days [02/27/2003]
I'm trying to convert a Gregorian date (e.g. Feb. 10, 1788) to the number of days that has passed since the implementation of the Gregorian Calender on October 15, 1582 (this being day 1).

Converting HH:MM to Minutes in Excel [06/25/2003]
Is there an easy method (i.e. any formula or a macro) for converting Hours:Minutes (HH:MM) to Minutes in Excel?

Converting Time [8/30/1996]
I have a clock that is "measured by 100", meaning 25=15 minutes, 50=30 minutes, etc. How do I convert this into "real time"?

Could There Be 8 Days in a Week? [04/24/2008]
If today is Tuesday, and I'm looking forward to next Tuesday, is it 7 days away or 8 days away?

Counting a Span Versus Finding a Difference between Two Numbers [06/03/2004]
Why is it that the difference between year 2012 and year 2003 equals 10 years but the difference between the numbers 2012 and 2003 equals 9?

Counting Friday the 13ths or Other Dates in a Year [12/17/2003]
What is the greatest possible number of Friday the 13ths that can occur in a year?

Dated Determination: Converting from the Julian Calendar to the Gregorian [02/09/2011]
A programming student seeks an algorithm that would convert Julian calendar dates to Gregorian, and back again. Doctor Vogler acknowledges the flexibility of using a common dating scheme as a base, then outlines how to leverage the offset between the two systems.

Define Warp in Lightyears [3/31/1995]
On Voyager, the new Star Trek show, they are 75 years from home. Their top speed is Warp 9.75. Can you define "Warp" in lightyears?

Different Yearly Calendars [09/30/2001]
How many years does it take before each calendar is used at least once? Start counting with the year 2001.

Elapsed Time and the Grouping Factor [03/08/2003]
Why can't you just subtract the two times given in a word problem and get the time elapsed?

Formula for Easter [06/12/1999]
Is there a formula for finding the month and the day on which Easter falls in a given year?

Formula to Compute One's Exact Age [05/31/2000]
Is there an equation to find a person's exact age on a given date, taking into account leap years?

Good Friday on the 13th [04/10/2001]
How many times has Good Friday fallen on the 13th?

How Long Does It Take to Count to a Billion? [03/28/2003]
Why people who need to deal precisely with long intervals (like astronomers and computer scientists) avoid using 'years' as a unit of time.

How Long is a Meter? a Second? [09/06/2001]
How is the length of a meter currently determined?

How Many Calendars Do I Need? [01/02/2002]
In 1980 I began collecting calendars, and I have done so every year since. What is the last year I must collect a calendar in order to have one that can be used for every year?

How Often Are There 5 Sundays in February? [02/27/2004]
How often are there 5 Sundays during the month of February?

Jewish Calendar [03/28/2002]
If the Jewish calendar has the same number of days each year, why do the holidays fall at a different time each year?

Julian Day Calculator [05/18/2003]
If I want to know my exact age in days without counting out the days, what would be the equation?

Light Year [08/09/1997]
How long (in miles) is a light year?

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