# Arithmetic Sequence - Series Questions

• Jan 12th 2012, 07:31 PM
Diesal
Arithmetic Sequence - Series Questions
How many terms for the arithmetic sequence {-3,2,7,...} must be added together for the sum of the series to be 116? - SOLVED, Thanks pickslides!

Also;

Find the least value of n for which Sn>10000 for the sequence {3,6,12...}

Finally

A ball is dropped from a height of eight feet. The ball bounces to 80% of it's previous height of each bounce. How high (to the nearest tenth of a foot) does the ball bounce on the fifth bounce?

I know I can logically solve some of these problems with logic, but I need to do it arithmetically. I don't necessarily need these solved, just the appropriate process to go about solving them.
• Jan 12th 2012, 07:39 PM
pickslides
Re: Arithmetic Sequence - Series Questions
For the first one, $\displaystyle 116 = \frac{n}{2}(2a+(n-1)d)$

What is a (the first term) and d (the common difference) in your sequence?

Once you know then solve for n.
• Jan 12th 2012, 07:44 PM
Diesal
Re: Arithmetic Sequence - Series Questions
I get to 116=n/2(5n-11) and I feel like I'm going to end up factoring a quadratic, is that correct?
• Jan 12th 2012, 07:46 PM
pickslides
Re: Arithmetic Sequence - Series Questions
I have the same feeling.
• Jan 12th 2012, 07:54 PM
Diesal
Re: Arithmetic Sequence - Series Questions
Alright, so n=8 and n=-29/5. I filled 8 in for n and got 116. You are a great human being for taking the time to help me. Thank you so much for the first answer!