00:01
So in this question, we say the population of a town is growing according to a differential equation, dy, d .d, t, equals ky.
00:08
The growth constant k is equal to 0 .07 per year.
00:13
The size of the population at the start of the year 2000 was 15 ,000.
00:18
Since the population is growing exponentially, they say the population in e or t is given by y equals 15e to the power of 0 .000.
00:30
0 .07 t.
00:32
Here the y is measured in thousands and t is measured in years since 2000.
00:39
In part a, they say what is the population of the town at the start of the year 2006? so 2006 is going to be t equals six and so what i'm going to do is just plug that in to this equation.
01:00
I have 15 to the power of .07 times six.
01:07
15e to the power of 0 .07 times six.
01:12
Now you get 22 .829.
01:16
Now, they did say i want the population.
01:19
This was in thousands.
01:22
So this is going to give you 22 ,829 .42.
01:33
That would be my population in the year 2006.
01:38
So we let t equals six.
01:41
In part b, what is the population of the town at the end of the year 2012? you've got to be careful.
01:49
So the end of 2012 is the same as the very beginning of 2013.
01:55
So i'm going to be plugging not 12, but 13, into this equation.
02:00
Getting y equals 15 e to the power of 0 .07 times 13.
02:10
And so i'm going to have the exact same setup, except my t is 13 instead of 6.
02:18
And now i'm getting 37 ,264 .8.
02:24
I'm getting 37 ,000, 37 ,264...