Question

What is the sum of the even number from 2 to 42 ?

Answer 1

here
a=2,tn=42,d=2

tn=a+(n-1)×d
42=2+(n-1)×2
42/2=2+(n-1)
21-2=n-1
19=n-1
n=20

Sn=n/2(a+tn)
S20=20/2(2+42)
S20=10×44
S20=440

therefore the sum of the even no. from 2 to 42 is 440.