Question

What is the sum of the first five terms of the series 35+30+25+...?

Answer 1

35+30+25+20+15=125

Answer 2

You can see each consecutive term has a difference of 5, right?
Your first term is 35.
Using the sum formula for an arithmetic series:
\[\frac{ n }{ 2 }(2a +(n-1)d)\]
a = first term
n = number of terms
d = difference between terms
You could just count it like above but it's nice to know the formula for when you are asked to find the sum of a much higher number of terms and it becomes more tedious to do by hand :)

Answer 3

Thank you to both of you :3 Very much help^^