Question

Find the sum of the first 5,000 odd numbers

Answer 1

Explanation:

this is an arithmetic sequence :

a1 = 1

an = an-1 + 2 = a1 + (n-1)×2

the sum of n terms of an arithmetic sequence is

S = n×(a1 + an)/2

n = 5000

an = a1 + 4999×2 = 9999

S = 5000×(1 + 9999)/2 = 5000×5000 = 25,000,000