Question

the sum of 60th term of 10, 20, 30, 40,........ is

Answer 1

sum(s) = n/2 { 2a+(n-1)d}
= 60/2 { 10×2 + ( 60-1) 10}
= 30 { 20+ 590}
= 30× 610
= 18300

Answer 2

S60=??

by formula:

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

S60=60/2 [2×10+(60-1)10]

S60=30 [20+590]

S60=30 [610]

S60=18300