See also the
Dr. Math FAQ:
calendar & days
of the week
3D and higher
Browse Elementary Calendars/Dates/Time
Stars indicate particularly interesting answers or
good places to begin browsing.
Selected answers to common questions:
A million/billion seconds.
- How to Tell Time [11/23/1998]
How do you read time that is not exactly on the hour or half hour? For
example, what does 1:35 look like?
- 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?
- 7-, 9-Sided Polygons [9/13/1996]
What is the name of a 7-sided figure? a 9-sided figure? Is one of these ever called a septagon? If "septi" means seven, why is September
the 9th month of the year?
- 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?
- Calculating Timecards [08/03/1999]
Is there a formula to find how many hours a person worked?
- Converting Clock Time to a Decimal [06/04/1999]
How can you convert a time range to a decimal?
- 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
- 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?
- Diagramming Days [08/28/2003]
What day of the week was yesterday if 5 days before the day after
tomorrow was Wednesday?
- Elapsed Time [11/26/2002]
How much time is there between 6:45 and 9:02?
- 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?
- How Long is 1000 Seconds? [02/18/2005]
How long does it take to count to one thousand counting one number per
- 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?
- Midnight on Which Day? [04/12/2003]
I assumed midnight on Sunday meant Sunday at 12:00 AM. So three and
half days later would be Wednesday at 12:00 PM or noon...but I was
told it was Thursday at noon...
- Military and Nautical Time [06/26/2000]
How do you convert nautical (military) time to standard time?
- Military Time, Spoken [10/18/2002]
I need to know the correct way of saying the 24-hour clock system.
- Numbers: Cardinal, Ordinal, Nominal? [10/25/1999]
Which group of numbers - cardinal, ordinal or nominal - does "time" fit
into? Are there other types of numbers as well?
- Seconds since 1980 [08/08/2002]
How can I work out the number of seconds since 1980, taking leap years
- Subtracting Time [02/27/2001]
A marathon runner crossed the finish line after running for 2 hours, 48
minutes, and 12 seconds. She crossed the line at 9:18:12 A.M. When did
the marathon start?
- Subtracting Time Expressions [10/09/2005]
How do I subtract two amounts of time, like
5 years, 21 days, 4 hours, 32 minutes, 17 seconds
- 2 years, 93 days, 7 hours, 47 minutes, 24 seconds
- Telling Time: A.M. and P.M. [10/30/2001]
What do A.M. and P.M. mean?
- Time Zones [05/09/2003]
How do time zones work?
- What Day of the Week Was a Given Date? [01/05/2006]
Is there a simple way to figure out what day of the week any date in
history fell on?
- When Does Your Birthday Fall on the Day You Were Born? [02/20/2004]
I'm curious how many years pass before your birthday falls on the day
of the week you were born?
- Why Does 1 Degree Equal 60 Minutes? [07/28/2004]
In 60 minutes, the minute hand of a clock makes a full circle, which
is 360 degrees. How can 60 minutes equal 1 degree when measuring angles?