Question

find the sum 1+3+5+...+52(the sum of all odd numbers from 1 to 51) without actually adding them

Answer 1

I don't know exactly but I think that the answer should be 2704

Answer 2

hi fend ,
a=1 ,d= 3-1 = 2
Now,
An= 51
or, 1+(n-1)2=51
or, 1+2n-2=51
or,2n-1=51
or,2n=52
or,n=26
Then,
Sn=S26=26/2(1+51)
=26/2×52
= 13×52
=676