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1. I am doing a past paper about compound interest. I know its easy but i just simply can not understand this for some reason.

Question:
Jaspir invested £2400 for n years in a savings account.
He was paid 7.5% per annum compound interest

At the end of the n years he had £3445.51 in the savings account

b) Work out the value of n

My workings:

Well i got the equation for Compound interest : Total = P x (1+x) ^n

Then i substituted: 2400 x (1.075)^n = 3445.51

Expanded and tried to get n on its own : 1.075^n - 3445.51 / 2400

How do i get n on its own?

Thanks

-JFinzz
2. (Original post by JFinzz)
I am doing a past paper about compound interest. I know its easy but i just simply can not understand this for some reason.

Question:
Jaspir invested £2400 for n years in a savings account.
He was paid 7.5% per annum compound interest

At the end of the n years he had £3445.51 in the savings account

b) Work out the value of n

My workings:

Well i got the equation for Compound interest : Total = P x (1+x) ^n

Then i substituted: 2400 x (1.075)^n = 3445.51

Expanded and tried to get n on its own : 1.075^n - 3445.51 / 2400

How do i get n on its own?

Thanks

-JFinzz
How did you get 3445.51
3. (Original post by steve2005)
How did you get 3445.51
It was in the question. That was his compound interest after the n years
4. (Original post by JFinzz)
I am doing a past paper about compound interest. I know its easy but i just simply can not understand this for some reason.

Question:
Jaspir invested £2400 for n years in a savings account.
He was paid 7.5% per annum compound interest

At the end of the n years he had £3445.51 in the savings account

b) Work out the value of n

My workings:

Well i got the equation for Compound interest : Total = P x (1+x) ^n

Then i substituted: 2400 x (1.075)^n = 3445.51

Expanded and tried to get n on its own : 1.075^n - 3445.51 / 2400

How do i get n on its own?

Thanks

-JFinzz
For this, you don't actually need to get n on its own, you just need to keep applying the compound interest to the values at the end of each year until you get 3445.51. Then the number of times you had to do this is your value for n.
5. I can't remember if logs is GCSE or not, if it isn't simply use trial and error to see what value of n makes 1.075^n = 3445.51/2400
6. (Original post by JFinzz)
Then i substituted: 2400 x (1.075)^n = 3445.51
This is right.

Divide both sides by 2400 to obtain.

Try integer values of n in order. It won't take you long.
7. log 1.425 / log 1.075

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