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?
You're guessing. Use the formula.
You START with 900. Why would there be only 900 still after 12 days?
Think about doubling.
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.