What is the sum of numbers from 1 to 100?

Question:

Find the sum of  1, 2, 3,4……………….98,99,100

Answer :

Restructure the above as

(1+100) +(2+99) + (3+98) + ……… ( 50+51)=  (101)+(101)…………………..+ (101)  = 50 x 101=5050

This is basically the sum of an arithmetic series formula

(A+L) x N/2

A=First term

L=Last term

N=Number of terms

If you are asked the sum between 50 and 100 then the answer will be

(50+100) x 51/2 =  150 x 25.5 = 3825.