A bacteria divides every half-hour to produce two new bacteria. If 30 bacteria start in a petri dish, how many will be present at the beginning of the 5th hour?

This is a squencing problem that I am unsure of how to work... I have formulas but I'm not sure which one it fits with and they are as follows:
s=a1 (1-r^n)/(1-r)
an=a1 (r^n-1)

After 1/2 hour, you will have 2 bacteria for every one bacterium, at the end of 1 hour, you will have 4. How many doubling times occur in 5 hours (n)? You have 2^n bacteria for every one you started with. So, multiply that by the number you started with.

Your second formula is the correct one. Just make sure you count the number of generations correctly.

It worked! Thanks