Turn on thread page Beta
 You are Here: Home >< Maths

# C2 - Geometric Series help. watch

1. Hi guys,

I am struggling on this geometric series question (I have attached the image of the question and mark scheme). Why in the mark scheme have they used arn as opposed to arn-1, which I thought was the correct formula? My answer ended up being 16.24... as opposed to 15.24... which is what is in the mark scheme. Can someone please explain?

Thanks
Attached Images

2. (Original post by DhylanP - CRGS)
Hi guys,

I am struggling on this geometric series question (I have attached the image of the question and mark scheme). Why in the mark scheme have they used arn as opposed to arn-1, which I thought was the correct formula? My answer ended up being 16.24... as opposed to 15.24... which is what is in the mark scheme. Can someone please explain?

Thanks
The only thing you've done wrong is to forget that, the way you've done it, n = 1 corresponds to the year 2000. Then, if we denote the year as Y, Y = n + 1999. Then, when n = 16, Y = 2015.

The mark scheme is perhaps a little unconventional in (apparently) denoting n = 1 as the year 2001 and taking the value that year as ar^1.
3. Hi,

I'm sorry but I don't understand exactly what you mean? Would you mind re-explaining? Sorry!

Thanks!
4. (Original post by DhylanP - CRGS)
Hi,

I'm sorry but I don't understand exactly what you mean? Would you mind re-explaining? Sorry!

Thanks!

N = 1 corresponds to year 2000
so
N = 2 corresponds to year 2001
N = 3 corresponds to year 2002
etc
N = 16 corresponds to year 2015

From what I can see, 2015 is the required answer.
5. Hi,

Yeah, I finally realised this. Can't believe how oblivious I was haha!

Turn on thread page Beta

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: February 13, 2018
The home of Results and Clearing

### 4,439

people online now

### 1,567,000

students helped last year
Today on TSR

### IT'S TODAY!

A-level results chat here

### University open days

1. Bournemouth University
Clearing Open Day Undergraduate
Fri, 17 Aug '18
2. University of Bolton
Fri, 17 Aug '18
3. Bishop Grosseteste University
Fri, 17 Aug '18
Poll
Useful resources

## Make your revision easier

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

Can you help? Study help unanswered threads

## Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE