infinitemoes
Please help! What is the sum of the series? 20 on top and n1 on the bottom of ∑(5n)



This Question is Closed

Dido525
Best Response
You've already chosen the best response.
0
did you mean n=1?

Dido525
Best Response
You've already chosen the best response.
0
@infinitemoes

infinitemoes
Best Response
You've already chosen the best response.
1
no it's a n1 on the bottom of the sigma.

mrbarry
Best Response
You've already chosen the best response.
1
\[\sum_{n1}^{20} (5n)\]

infinitemoes
Best Response
You've already chosen the best response.
1
yes exactly like that

mrbarry
Best Response
You've already chosen the best response.
1
It should be n=1 I am certain.
If we did this "manually" we would have 4 + 3 + 2 + ...
Right?

infinitemoes
Best Response
You've already chosen the best response.
1
alright..

mrbarry
Best Response
You've already chosen the best response.
1
This is an arithmetic sequence b/c we are adding 1 over and over. There is a formula to solve this, Arithmetic Series Formula.
Do you know it?

infinitemoes
Best Response
You've already chosen the best response.
1
I think I got the answer. 110

mrbarry
Best Response
You've already chosen the best response.
1
Let's see. The formula says: 1/2 the number of items times (first term + last term)
1/2 (20) (4 + 15)
10 (11)
Good job.

infinitemoes
Best Response
You've already chosen the best response.
1
thank you! :)

mrbarry
Best Response
You've already chosen the best response.
1
You are welcome. All done? Thanks for the medal.

infinitemoes
Best Response
You've already chosen the best response.
1
Well I do have a couple more questions, but I'm gonna post them separate to this post.

mrbarry
Best Response
You've already chosen the best response.
1
Of course.