please help me find linear function modelling number of

[georgebaseball]

I am having a very hard time with this problem:

I am given a graph showing the number of persons below the poverty threshhold in a given year. On the y axis are the million of people and in the x axis are the years.

For the year 1996, the graphs shows that there were 36.5 million people below the poverty threshhold; in 2000, there were 31.1 million people. The exercise then asks me:

Using 1996 as a reference year, determine a linear function that can be used to estimate the number of people below the poverty threshold for the years 1996 through 2000. In the function, let "t" represent the number of years after 1996.

First, I replaced "1996" for 1 and "2000" for 5. I use the slope formula to get:

. . .m = (31.1 - 36.5)/(5 - 1) = -1.35

Then I used the point-slope form of a linear equation to get:

. . .y - 31.1 = -1.35(x - 5)
. . .y - 31.1 = -1.35x + 6.75
. . .y = -1.35x + 37.85

But the book says the correct answer is y = -1.35x + 36.5. What am I doing wrong?

Thank you!
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Edited by stapel -- Reason for edit: formatting, spelling

 

[skeeter]

Using 1996 as a reference year, determine a linear function that can be used to estimate the number of people below the poverty threshold for the years 1996 through 2000. In the function, let "t" represent the number of years after 1996.

the directions say to use 1996 as year zero ... i.e. t = 0 , not t = 1.

you have a set of ordered pairs ...

(0, 36.5) and (4, 31.1)

m = (31.1 - 36.5)/(4 - 0) = -5.4/4 = -1.35

you have a slope and y-intercept ... the equation is

P = -1.35t + 36.5

where P is the number of people (in millions) who fit the poverty level and t is the year after 1996.

 

[georgebaseball]

Ohh I got it! thank you so much skeeter !