Question

what is the sum of 1 to 100 numbers .? natural number

Answer 1

n (n+1)/2............

Answer 2

ANSWER WITH EXPLANATION

You want that I should find out the sum of 1 to 100 natural numbers, which means that I have to find out the sum of first 100 natural numbers. 
Well, I am going to use a formula to calculate the same. 

Let the number of natural numbers be $n$. 
Then, $n=100$. 

Now, I am going to put this value into a formula. See now. 
$\frac{n(n+1)}{2}$
$=\frac{100(100+1)}{2}$
$=\frac{100*101}{2}$
$=5050$

Well, this formula is used to find out the sum of first $n$ natural numbers, if $n$ represents the number of natural numbers. 

∴ The sum of the first 100 natural numbers is 5050. 

Hope this may help you. 

If you have any doubt, then you can ask me in the comments.