Question

6+11+16+21+26+……+71=?

Answer 1

a= 6
d= 5
a_n= 71
 a_n = 6+ (n-1)5
⇒n=14
Sn= n/2(a+a_n)
     7 x 77 
    = 539

HOPE U LIKED THE ANSWER :D