# What day will it be after a 100 days

• Jan 16th 2010, 06:26 AM
ethio
What day will it be after a 100 days
How can I work out what day of the week it'll be after x amount of days?
Some kind of formula to this......
• Jan 16th 2010, 06:45 AM
awkward
Quote:

Originally Posted by ethio
How can I work out what day of the week it'll be after x amount of days?
Some kind of formula to this......

Number the days of the week from 0 to 6 (you get to choose which day is day zero), then add x to today's day-of-the-week number, doing all arithmetic modulo 7.
• Jan 16th 2010, 07:40 AM
ethio
Sorry for this but can you give me an example? say...any number of days from today, with a full workout.
• Jan 16th 2010, 09:36 AM
Plato
Quote:

Originally Posted by ethio
How can I work out what day of the week it'll be after x amount of days? Some kind of formula to this......

As was suggested number the days. $\boxed{\begin{array}{lllllll} {Su} & M & T & W & {Tr} & F & S \\\hline 0 & 1 & 2 & 3 & 4 & 5 & 6 \\ \end{array} }$
If we divide 25 by 7 we get a remainder of 4.
If today is Sunday then in 25 days it will be Thursday: 0+4=4. Four is Thursday.
But if today is Friday in 25 days it will Tuesday: 5+4 divided by 7 has a remainder of 2 and 2 is Tuesday.

So divide x by 7 to get a remainder. Add that to the number of the day and then find the remainder when divided by 7 that number day in x days later.
• Jan 16th 2010, 01:13 PM
ethio
Thank you both.