aryx

Has anyone ever asked you to add up all the numbers from 1 to some high number?
For example, add all the numbers from 1 to 100. What is your answer.

Instead of actually adding up all those numbers, there's a really quick and easy way to get the answer.
If your multiplication skills are decent, you should be able to race one of your friends (or even a group!) and always come out the fastest (so long as no one else knows this same trick).

First, you are going to take your highest number (in this case, 100) and add 1 to it.
Next, you are going to multiply your highest number (still 100 here) to the new number (101).
In this case, 100 * 101 == 10100.
Finally, you are going to devide the new number by 2 (or in half, whichever way makes it easier for you to remember.
So, 10100 / 2 == 5050.
And there's your answer.
Here's the formula for you math minded wizards:
( X * ( X + 1 ) ) / 2

Remember, this only works if you start from 1, and have to add all the numbers up to your X.

Now let's try 42 (because we all know that 42 is the answer to Life, the Universe, and Everything!)
( 42 * ( 42 + 1 ) ) / 2 == ( 42 * 43 ) / 2 == 1806 / 2 == 903

Now tell me what the answer is to my favorite number, 36!