00:01
So in this problem, we're told that in the year 2009, you have 90 songs in your itunes playlist, in the year 2011, you have 110 songs, and in the year 2014, you're back down to 90 songs.
00:11
So in part a, what they want us to do is find the average rate of change per year in the number of songs in your favorite itunes playlist from the year 2009 till the year 2011.
00:23
Well, remember, to find the average grade of change means that we need to find the change in the number of songs over the time period.
00:30
So what we're going to do is we're going to start with the number of songs in 2011, because that's how many you'll end up with, minus the number of songs in 2009, which is 90.
00:39
And we're going to divide that by the change in time, which would be the year 2011 minus 2009.
00:45
And now we just need to simplify.
00:47
Well, 110 minus 90 is 20.
00:50
2011 minus 2009 is 2.
00:53
And then we have 20 divided by 2, which is 10, which means that there's an average rate of change of 10 songs per year.
01:00
All right.
01:01
So now in part b, we want to do the same thing, except we want to go from the year 2011 till the year 2014.
01:08
So again, we're going to find the change in the number of songs.
01:11
So we start with 2014, so 90 minus the number of songs in 2011, which is 110...