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# C2 Geometric sequences - interest questions?? Watch

1. I've been looking at some of the C2 interest questions, which could come up this year as they haven't in recent years. They seem a very strange. Does anyone have any good methods for questions like this:

Sally invests £200 into a bank account, which has interest of 6% per annum. She invests a further £200 at the beginning of each year.
a) How much does she interest does she earn in year 7?

I did:
200(1.06)^7 = £300.73
£300.73-£200 = £100.73

b) What is the total sum in the bank account after 13 years?
I did:
200(1.06(1-1.06^13) / (1-1.06) = £4003

Can you guys verify these and advise on any better methods?
I've been looking at some of the C2 interest questions, which could come up this year as they haven't in recent years. They seem a very strange. Does anyone have any good methods for questions like this:

Sally invests £200 into a bank account, which has interest of 6% per annum. She invests a further £200 at the beginning of each year.
a) How much does she interest does she earn in year 7?

I did:
200(1.06)^7 = £300.73
£300.73-£200 = £100.73

b) What is the total sum in the bank account after 13 years?
I did:
200(1.06(1-1.06^13) / (1-1.06) = £4003

Can you guys verify these and advise on any better methods?
I would have done the same tbh. Since we are on the topic can you assist me with the following question
A savings scheme pays 5% per annum compound interest. A deposit of £100 is invested in this scheme at the start of the year.
a). Show that at the start of the third year,after the annual deposit has been made, the amount in scheme is £315.25

I can't seem to do it?
3. (Original post by Super199)
I would have done the same tbh. Since we are on the topic can you assist me with the following question
A savings scheme pays 5% per annum compound interest. A deposit of £100 is invested in this scheme at the start of the year.
a). Show that at the start of the third year,after the annual deposit has been made, the amount in scheme is £315.25

I can't seem to do it?
I get 318.24
4. (Original post by maths learner)
I get 318.24
What did you do? The answer seems wrong to me.
5. (Original post by Super199)
I would have done the same tbh. Since we are on the topic can you assist me with the following question
A savings scheme pays 5% per annum compound interest. A deposit of £100 is invested in this scheme at the start of the year.
a). Show that at the start of the third year,after the annual deposit has been made, the amount in scheme is £315.25

I can't seem to do it?
You know for part b can't you use (a-r^n)/(1-r) and use r as 1.06?

Just a suggestion, let me know if it's wrong.
6. (Original post by Super199)
I would have done the same tbh. Since we are on the topic can you assist me with the following question
A savings scheme pays 5% per annum compound interest. A deposit of £100 is invested in this scheme at the start of the year.
a). Show that at the start of the third year,after the annual deposit has been made, the amount in scheme is £315.25

I can't seem to do it?
100(1-1.05^3)/1-1.05 = £312.25
This is slightly different to my example as they didn't put money in at the start of each year
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