A colony of bacteria starts with 900 organisms and double every 12 days
It follows that there will be:
how many organisms after 24 days....I assume 1800 right?
how many after 2 days
how should I approach it?
Doubles every 12 days. There is a standard exponential version, but sometimes I like just writing it down...
$\displaystyle 900*(2)^{Days/12}$
Test it.
$\displaystyle 900*(2)^{12/12} = 900*2^{1} = 900*2 = 1800$
Use it.
$\displaystyle 900*(2)^{24/12} = 900*2^{2} = 900*4 = 3600$ Oops. You had better check that.
Use it again.
$\displaystyle 900*(2)^{2/12} = ???$
You're guessing. Use the formula.
You START with 900. Why would there be only 900 still after 12 days?
Think about doubling.
Start: 900
12 days: 900*2 = 1800
24 days: 2*12 days = 900*2*2 = ??
Seriously, WRITE DOWN a working formulation. Don't try to do it in your head or on your calculator. Let the notation help you. Allow the algebra to soak into your brain and pour over your soul...
Ahem...Sorry, I got a little poetic, there.