Bacteria are grown in a petri dish. The amount of bacteria doubles in size every 2 days. If it took 16 days for the bacteria to cover the whole petri dish, how many days did it take for the bacteria to cover one quarter of the petri dish?
Let's solve this two ways.
First if it doubles each day, then that means that if we step backwards in time it halves each day. If on day 16 it was twice as much as day 15, then on day 15 it was half as much as day 16. Similarly day 14 was half a much as day 15 and so forth. So if day 16 was 100% covered, then day 15 was half of 100% covered, or 50% and day 14 was half as much as day 15, so 25% or one quarter. This is probably the expected way to solve it.
I have doubts about my answer and your help would be very helpful.