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MaleVip
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#1
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I am trying to do geometric sequence question..I NEED URGENT HELP PLES!!

This is the question

"I invest £A in the bank at a rate of interest of 3.5% per ammum. How long will it be BEFORE i double my money?

I seriously dont understand what the word before implies .

My steps are like
A * (1.035)^n-1 < 2A
n<21.148
Hence n = 21

But the acutal answer is 20.15

I tried the solution bank but didn't find it helpful.

Thank You
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Kevin De Bruyne
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(Original post by MaleVip)
I am trying to do geometric sequence question..I NEED URGENT HELP PLES!!

This is the question

"I invest £A in the bank at a rate of interest of 3.5% per ammum. How long will it be BEFORE i double my money?

I seriously dont understand what the word before implies .

My steps are like
A * (1.035)^n-1 < 2A
n<21.148
Hence n = 21

But the acutal answer is 20.15

I tried the solution bank but didn't find it helpful.

Thank You
What does n represent in your equation?

Think about what it means when n = 1, n= 2 etc in your equation.
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Xenon17
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(Original post by MaleVip)
I am trying to do geometric sequence question..I NEED URGENT HELP PLES!!

This is the question

"I invest £A in the bank at a rate of interest of 3.5% per ammum. How long will it be BEFORE i double my money?

I seriously dont understand what the word before implies .

My steps are like
A * (1.035)^n-1 < 2A
n<21.148
Hence n = 21

But the acutal answer is 20.15

I tried the solution bank but didn't find it helpful.

Thank You
For this you don't need A *r^(n-1) but A *r(n)
Think of it this way you invest A and after 1 year you'll have A*1.035 so your method seems correct except the -1 part
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MaleVip
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(Original post by SeanFM)
What does n represent in your equation?

Think about what it means when n = 1, n= 2 etc in your equation.
n is the number of years


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Kevin De Bruyne
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(Original post by MaleVip)
n is the number of years


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Right.. so when n=1, that's one year, what does the left hand side of your equation suggest? (what I am trying to hint at has been given above already)
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MaleVip
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(Original post by SeanFM)
Right.. so when n=1, that's one year, what does the left hand side of your equation suggest? (what I am trying to hint at has been given above already)
Okay i see what you mean.. Kinda..
But then..


"Find which term in the progression 3,12,48... Is the first to exceed 1000000?"

The actual steps for the answer;

3*(4)^n-1>1000000

Why isnt it just 3*(4)^n>1000000
Like before??




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Kevin De Bruyne
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(Original post by MaleVip)
Okay i see what you mean.. Kinda..
But then..
How does this relate to the equation
Nth term = ar^n-1??


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So what is the first term? (n=1) and what does that term mean/signify, in the context of the question?

Hence what number term are you actually looking for, rather than 21? (With your method you don't have to do any extra calculations, just realise what your n's and n=21 means).
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