Question

In a straight highway the 1st, 2nd, 3rd,and so on traffic signals are fixed at a distance of 3km,5km,7km and so on . What is the distance of 10th traffic signal?

Answer 1

a=3km
d=2km
n=10
An= a+(n-1)d
=3+(10-1)2
=3+(9)2
=3+18
=21
Hence,the 10th traffic signal will be after 21km.