Question

Given l = a +(n-1)d find n if l = 31 a = 15 and d= 2

Answer 1

l=a+(n-1)d
31=15+(n-1)2
31=15+2n-2
31-13 = 2n
n = 18/2
n = 9

Answer 2

I=a+(n-1)d
31=15+(n-1)2
31=15+2n-2
31+2=15+2n
33-15=2n
∴n=18/2
∴n=9