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# C2: Logarithms and modelling graphs watch

1. Hi,

I am just stuck on the last few questions of logarithms, and was hoping you could help me answer them:

How many terms are there in these geometric sequences:
i) -1, 2, -4, 8, ... -16777216

I know that the common ratio is multiply -2 each time, but thats as far as I got.

ii) 0.1, 0.3, 0.9, 0.27, ... 4304672.1

Again, I know the common ratio is x3.

Soames Forstye states how many years it take to double your money at 7% interest. Given interest is paid yearly, at the end of the year, what number of years does he say?

I dont really understand this question at all.

Thank you for your help !!!
2. (Original post by cmab52)
Hi,

I am just stuck on the last few questions of logarithms, and was hoping you could help me answer them:

How many terms are there in these geometric sequences:
i) -1, 2, -4, 8, ... -16777216

I know that the common ratio is multiply -2 each time, but thats as far as I got.

ii) 0.1, 0.3, 0.9, 0.27, ... 4304672.1

Again, I know the common ratio is x3.

Soames Forstye states how many years it take to double your money at 7% interest. Given interest is paid yearly, at the end of the year, what number of years does he say?

I dont really understand this question at all.

Thank you for your help !!!
un = ar^(n-1) = -16777216
Where a = u1
Same for part ii)
3. (Original post by cmab52)
Hi,

I am just stuck on the last few questions of logarithms, and was hoping you could help me answer them:

How many terms are there in these geometric sequences:
i) -1, 2, -4, 8, ... -16777216

I know that the common ratio is multiply -2 each time, but thats as far as I got.

ii) 0.1, 0.3, 0.9, 0.27, ... 4304672.1

Again, I know the common ratio is x3.

Soames Forstye states how many years it take to double your money at 7% interest. Given interest is paid yearly, at the end of the year, what number of years does he say?

I dont really understand this question at all.

Thank you for your help !!!
Last q:
Here a = 1
r = 1.07
you are trying to find when Sn>2
4. (Original post by joostan)
un = ar^(n-1) = -16777216
Where a = u1
Same for part ii)
Thank you!!
5. (Original post by cmab52)
Thank you!!
No problem

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