Remark
You can use a formula to get the right answer. Otherwise you will use a lot of paper adding 100 numbers together.
Givens
A = 1
L = 100
n = 100 numbers to be added together. There are 100 numbers between 1 and 100 numbers inclusive.
Formula
Sum = (A + L)*n/2
Solution
Sum = (1 + 100)*100/2 Substitute in the givens. Add what is inside the brackets
Sum = (101) * 100 / 2 Divide by 2
Sum = 101* 50 Multiply
Sum = 5050 Answer