Question

Quantos termos tem a p.a (20,25,30,35...,5005?
qual formula devo usar nesse caso?

Answer 1

an=a1+(n-1).r
an=5005
a1=20
r=5
Assim temos:
an=a1+(n-1).r
5005=20+(n-1).5
5005=20+(5n-5)
5n-5=5005-20
5n-5=4985
5n=4985+5
5n=4990
n=4990/5
n=998