Zeller's congruence

Zeller's Congruence is a way to find out which day of the week any particular date falls on. It's like a magic formula that gives you the answer to a question about dates!

Now let's break this formula down into simple steps that even a 5-year-old can understand:

Step 1: First, you need to write down the date in a certain way: DD/MM/YYYY. DD represents the day, MM stands for the month, and YYYY represents the year.

Step 2: Next, you need to use a special formula called Zeller's Congruence. This formula works by dividing the parts of the date you just wrote down into different numbers that represent different things.

Step 3: Here's what each part of the date means:

- DD is the day of the month (for instance, 25th)
- MM represents the month (January is 1, February is 2, March is 3, and so on)
- Century number (The first two digits of the year. For example, the century number of 1854 is 18, and the century number of 2001 is 20.)
- The year number (The last two digits of the year. For example, the year number of 1854 is 54 and of 2001 is 01)

Step 4: After you've divided the parts of the date into those numbers, you can use them in the formula to find out what day of the week it is. The formula goes something like this:

DayOfWeek = (DD + [(13 * (MM + 1)) / 5] + YY + [(YY / 4)] + [(CC / 4)] - (2 * CC)) % 7

Don't worry if it seems a bit complicated. All you need to do is substitute the values of DD, MM, YYYY, and the century number (CC) and the year number (YY) in the formula and then solve it using simple arithmetic.

Step 5: Once you've done the math, you should get a number between 0 and 6. Each number corresponds to a day of the week, starting from Sunday (0), Monday(1), Tuesday(2), Wednesday (3), Thursday(4), Friday(5), and ending with Saturday(6).

And that's it! You now know how to use Zeller's Congruence to find out what day of the week any date falls on. Happy calculating!