The prize of a lottery is $100 in the first week, $200 in the second week, $400 in the third week,

No, Eddy. You're confusing the geometric sequence with an arithmetic sequence. The terms in an arithmetic sequence differ by the same amount (that's why it's called a common difference).

With geometric sequences, we call r the common ratio because (starting with the second term) the ratio of each term to the prior term is always the same: r. Here are four examples:

800/400 = 2
400/200 = 2
200/100 = 2
an / an-1 = 2

I forgot. Are you working with math textbooks now?

:)
Yes, Otis, thanks for your help and support. I have bought several book. Algebra and geometry. I'll take some pics and send them to you. They are a great source of guidance like you said. As I explain Mr mmm the moderator( who, by the way, stayed in touch with me while I was banned!), amazing guy who kept wanting to teach me things)) I got my bachelor's degree back in Cuba where i taught ESOL in a teacher's college. I got credentialed when i got here and turned out to have a us bachelor degree so I have the opportunity to take tests to become a teacher without having to incur a humongous debt going to college and in a lot less time studying on my own. Right now I am teaching ESOL at a public school in Miami FL( I was loading and unloading trucks for some time), but I want to become a math teacher , at least, from 5-to 9 math teacher. I have to pass a Pearson test for math teachers. 5 to 9 math test. I t is not that difficult but i am prepping for that non-stop.
 
One last question if I may:
using the formula we got the desired result,
Question: Why couldn't we get the same result doubling the amounts by every week until week number 10, like i tried to do in post 12 i think, why?. It is supposed to work out with addition too, right, or not? or I performed the addition in the wrong way. Just wondering.
 
Greetings Mr Khan, I did check it out with the formula and it checks out. The result is the same.
Sn= a(1-r^2) / 1-r
Omitting parentheses is a serious mistake. I am not sure why so many students are so careless about them. The consequences of this mistake are just as bad as omitting a negative sign or any other math error. In this case you put them back on the second line, but next time you'll forget. Parentheses are not a cosmetic thing to make your expressions look pretty. They are absolutely necessary to get the correct result.
 
One last question if I may:
using the formula we got the desired result,
Question: Why couldn't we get the same result doubling the amounts by every week until week number 10, like i tried to do in post 12 i think, why?. It is supposed to work out with addition too, right, or not? or I performed the addition in the wrong way. Just wondering.
Post 12 shows why your addition was incorrect - you didn't calculate all the individual amounts correctly.
 
Post 12 shows why your addition was incorrect - you didn't calculate all the individual amounts correctly.
Thank you very much, Mr lev. And you are right about parenthesis. I tend to forget them. I will have to keep an eye out for them. I am using post-it notes for things I can't forget to do. I'm starting to do the same with some of the math must-do's.
 
Books I have bought
 

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To Otis
 

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@Eddy

In many ways, math is a language. If you are trying to learn math in English, and English is not your first language, it may help to get math books in Spanish.
 
Yes, I agree. It is more difficult getting them though. But I watch a lot of videos in Spanish and visit a lot of websites in Spanish too.
Thanks, Mr Jeff, for the advice.
 
Even though, If I may say so myself, I have had a love affair with the English Language for a long time. Reading nonstop and studying grammar, reading dictionaries, looking up every term I do not know till I can say without hesitation or bragging that I would be really hard for someone to stump me with a word. And that is a loud step to take around educated people.
 
But I have fallen for Math!. I love the challenge. Words are not a challenge anymore. And I know knowledge when I see knowledge and you all have my deepest respect.
 
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