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

**kcwillia377** · March 23rd 2009, 04:20 PM

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)

**e^(i*pi)** · March 23rd 2009, 04:24 PM

Originally Posted by kcwillia377

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)

$20 \times 10^6 = 8 \times 10^6 (1.01)^n$

**guardofthecolor4ever** · March 23rd 2009, 04:24 PM

yeah that's the correct formula...i'm pretty sure...but i could be wrong

**kcwillia377** · March 23rd 2009, 04:32 PM

How do I solve for n?

**e^(i*pi)** · March 23rd 2009, 04:54 PM

Originally Posted by e^(i*pi)

I think it's ^n instead of ^(n-1)

$20 \times 10^6 = 8 \times 10^6 (1.01)^n$

Originally Posted by kcwillia377

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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