Need to make an equation

[maxiffer]

Im looking to make an equation.
It says "With a population of 500 organisms, a growth rate of 2, and a growth period to achieve this rate of 6 hours. Assuming that none of the organisms die, this would imply that this population would double in size every 6 hours. Thus, after allowing 6 hours for growth we would have 1000 organisms."
I tried the growth a decay formula but it didn't give me 1000 so does anyone know the equation?

 

[tue]

If i read the question correctly, that would be something like:

P_t = P₀ x 2^t

Where P = population and t = time measured in 6 hours. If the time is 6 hours, the population is:

P₁=500 x 2¹ = 500 x 2 = 1000

if 6 hours passes again, the population is:

P₂=500 x 2² = 500 x 4 = 2000

and so on