Question

find the sum of first 123 even natural numbers

Answer 1

The number series 2, 4, 6, 8, 10, 12, .  .  .  .  , 246.
The first term a = 2
The common difference d = 2
Total number of terms n = 1
 apply the input parameter values in the AP formula
Sum = n/2 x (a + Tn)
= 123/2 x (2 + 246)
= (123 x 248)/ 2
= 30504/2
2 + 4 + 6 + 8 + 10 + 12 + .  .  .  .   + 246 = 15252

Answer 2

15252 is yours answer