1. Two questions sort of.

Would it be right for me to assume X is positive for

and get to get X =5 as an answer.

and In Media-eval times there were 10,000 people living in a city that was struck by a plague. the number of people living after 6 days was 8,500 and after 12 days 7,225.
How would you determine the event is exponential and find the number of people living after 18 days.

if i set up my chart
0-10,000
6-8,500
12-7,225
18-X

I found a common ratio of .85 with help from some one else and after that I got kind of lost. (attempted an equation which didn't work)

2. Re: Two questions sort of.

Firstly, yes x=5

Plots the points, does it look exp?

Then consider the model $P = P_0 \times A^{kt}$ where population (P) is a function of time (t).

It should be clear that $P_0 =10000$

Now use the other two points given to find A & k