00:01
State census bureau uses demographic information to set a poverty threshold that is used in to determine how many americans are living in poverty based on annual income.
00:12
For an individual on their own, the poverty threshold was 4 ,190 in 1980 and has increased about $220 per year since then.
00:25
What piece of information in the problem is the rate of change? so that is how much per year that it has increased.
00:32
So that's the $220 per year.
00:40
What would represent a linear function modeling the poverty threshold? so y equals it would be 220x plus and then 4 ,190.
00:56
When modeling the information that changes with time, we almost never use the actual time.
01:02
Whether it's clock time or year as input.
01:06
Instead, we choose a beginning time for the problem and call that x equals zero.
01:13
In this case, we would decide that x corresponds to 1980.
01:19
Since that's the earliest time we have for information.
01:23
In that case, what is the y intercept of the function? so that's 4 ,190 is the y intercept.
01:29
Write a linear function that describes the poverty threshold in dollars in terms of years after 1980.
01:38
So, y equals 220x plus 4 ,190 and the year that it will pass 15 ,000 per year...