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

1. ## 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)

2. 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)

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

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

4. How do I solve for n?

5. 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:

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

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