Question

Find the sum of first 123 even natural numbers

Answer 1

The number series is in the form 2,4,6,8,10,12,14,16,18,20,…….

Series is in A.P. Here a=2, d=2 and given n=123.

S =(n/2)[2a + (n- 1)d]

S=(123/2)[2*2+(123–1)*2]

=(123/2)*2[2+122]

=123*124

=15,252.

Answer 2

These numbers form an AP


$a = 2 \\ d = 2 \\ n = 123 \\ s = \frac{n(2a + (n - 1)d)}{2} = 15252$