Question

Which term of ap 21 ,42,63 ,84.....is 420

Answer 1

hope this answer will be helpful ^_^

Answer 2

Answer:

a=21

d=42-21=21

an=420

an=a+(n-1)×d

=21+(n-1)×21=420

(n-1)×21=420-21=399

(n-1)=399÷21=19

n=19+1=20

so 20th term is a a.p