SOLUTION: Hi there, someone helped me earlier this week and it was awesome! Thank you! Here's my question... It's about Arithmetic Sequences and finding the nth term. Chem deposi

Algebra ->  Sequences-and-series -> SOLUTION: Hi there, someone helped me earlier this week and it was awesome! Thank you! Here's my question... It's about Arithmetic Sequences and finding the nth term. Chem deposi      Log On


   

Question 830780: Hi there, someone helped me earlier this week and it was awesome! Thank you!
Here's my question...
It's about Arithmetic Sequences and finding the nth term.
Chem deposited $115 into a savings account. Each week thereafter, he deposits $35 into the account.
A. Write the formula to find the total amount Chem has deposited for n weeks after his initial deposit.
B.How much had Chem deposited 30 weeks after his initial deposit?
I am using the formula: a_n = a_1 + (n-1)d
a_1=115
d=35
I got 35n + 80; $1,130
BUT...the book answer says 35n + 115; $1,165
I am wondering if I'm reading the problem wrong and the key is how much he deposited "after" the initial deposit. Thanks so much for answering my question!
Isabella
Found 2 solutions by richwmiller, rothauserc:
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
You are wrong. The book is right.
The first day (which is not a week) 115 was deposited
after one week 35 is added
after two weeks another 35 is added
after 30 weeks how much is there?
read the question carefully
"30 weeks after his initial deposit"
one week after the first 35 is added
You are making it more complicated than it need be
t=35n+115

Answer by rothauserc(4718) About Me  (Show Source):
You can put this solution on YOUR website!
use the following formula
a_n = a_0 + (n)d
where a_0 = 115, n = 30, and d = 35
a_n = 115 + (30 * 35)
a_n = 115 + 1050
a_n = 1165
30 weeks after initial deposit, means that n = 30