Since your question starts with the number 1, we can decide if we want to handle that specific series (even, 100 numbers) or add the 0 to make it odd without affecting the total sum.

I’ll do both.

For the odd series:

0 + 100 = 100

1 + 99 = 100

…

48 + 52 = 100

49 + 51 = 100

The pairwise sum is 100.

The number of pairs are 50.

The sum of all pairs are 50*100 = 5000

We add the unpaired center number 5000 + 50 = 5050

For the even series:

1 + 100 = 101

2 + 99 = 101

…

49 + 52 = 101

50 + 51 = 101

The pairwise sum is 101.

The number of pairs are 50.

The sum of all pairs are 50*101 = 5050

No unpaired center number

Another Solution of What is the total number of digits from 1 to 100?

Sum of Numbers Starting from 1 in a interval of 1 is given by

Sum=N×(N+1)/2

N= Last Number i.e. 100 here

Therfore ,

Sum =100×101/2

=5050