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Math Help - Do I have the formula right? How do I solve for n?

  1. #1
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    Exclamation Do I have the formula right? How do I solve for n?

    A population of 8 million increases at a rate of .1% every month. In how many months will it reach 20 million?


    Is the formula:

    20000000=8000000*(1.01)^(n-1)
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  2. #2
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by kcwillia377 View Post
    A population of 8 million increases at a rate of .1% every month. In how many months will it reach 20 million?


    Is the formula:

    20000000=8000000*(1.01)^(n-1)
    I think it's ^n instead of ^(n-1)

    20 \times 10^6 = 8 \times 10^6 (1.01)^n
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  3. #3
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    yeah that's the correct formula...i'm pretty sure...but i could be wrong
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  4. #4
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    How do I solve for n?
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  5. #5
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by e^(i*pi) View Post
    I think it's ^n instead of ^(n-1)

    20 \times 10^6 = 8 \times 10^6 (1.01)^n
    Quote Originally Posted by kcwillia377 View Post
    How do I solve for n?
    1.01^n = \frac{5}{2}

    Take logs:

    n\ln(1.01) = ln{\frac{5}{2}}

    n = \frac{ln(2.5)}{ln(1.01)} = 92.1
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