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## #1 This is Cool » How to be the next walking calendar? » 2011-03-02 00:32:10

tangent
Replies: 1

Ever thought that you can be a walking calendar? What I mean is that when someone ask you what the day is for a certain date, you will be able to tell whether it's a Monday, a Tuesday, a Wednesday and so on without a calendar.

You know when someone asks you for a definition of a word, and you can give the definition, you are a walking dictionary.

If someone asks you to calculate a certain operation of numbers and you can give the answer, you must be a walking calculator.

But what about if you can tell the day for any date in the past or in the future, then you must be the WALKING CALENDAR?

Is that really possible?

Oh yea!

Enjoy, learn the trick and be the NEXT WALKING CALENDAR!

## #2 Re: Help Me ! » prime numbers ` » 2011-03-01 23:44:25

The quickest way to know whether a number is prime aside from using the sieve of eratosthenes method is:
1. Find the square root of the number (e.g. 179, square root of 179 is approximately 13)
2. Try to divide 179 by any of the prime numbers up to 13 in this case, so use 7, 11 and 13 only.
Definitely if the number ends in 5, then it's composite, and if the sum of the digits of the given number is a multiple of 3, then it's divisible by three
3. Since in my example, 7, 11 and 13 does not divide 179, then 179 is prime.

Note, all even numbers greater than 2 are composite numbers, and only numbers ending in 1, 3, 7 or 9 are possible prime, but mostly not.

Make sure to always check whether it's divisible by 3 first up to the nearest square root of the given number.

## #3 Introductions » Hello Math lovers » 2011-02-28 12:40:56

tangent
Replies: 2

Hi everyone,

Tangent here, this is my first time to ever join a forum. I hope to make some friends who are also mathematical minded. I love doing all sorts of math especially mental math. I'm a math tutor and I love teaching math to any body who is willing to learn.