Question

Find sum of first 10 terms of a.p 3,15,27,39

Answer 1

Answer:

n=10

common difference =a2-a1 =15-3=12

a10,an=a1+9×common difference

=3+9×12

=111

s10 = n/2(a1+an)

=10/2(3+111)

=10/2×114

=10×57

=570