Can someone show me how to do this?
Find the sum of the given arithmetic series.

25 + 18 + 11 + 4 + ... + (–38)

Question

Can someone show me how to do this?
Find the sum of the given arithmetic series.
 
25 + 18 + 11 + 4 + ... + (–38)

anonymous · Answer

$$S _{n} =\frac{ n }{ 2 }(a _{1} + a _{n})$$ is your formula.

n is the number of terms
a1 is the first term
an is the last term

Can you get started now?  I am still here.

anonymous · Answer

Well I got stuck because im not sure how to find the number of terms

anonymous · Answer

any help? @mrbarry

anonymous · Answer

$$a _{n} = a _{1} + (n-1)d$$ is what we need now.

Everything has the same meaning.  d is the difference between consecutive terms. 
Can you roll now?

anonymous · Answer

Oh okay I understand what I need to do