Question

find the sum of natural numbers from 100-400​

Answer 1

a (first term) = 100

an (last term) = 400

d (common difference) = 1

an = a + (n-1)d

or, 400 = 100 + (n-1)1

or, 400 - 100 = n-1

or, 300 + 1 = n

or, n = 301

Sum = n/2 (a + an)

= 301/2 (100 + 400)

= 301/2 (500)

= 75250

The sum of naturals numbers from 100 to 400 is 75250.