Practice!

Sample Problem

x

6

12

18

24

30

36

42

y

120

60

40

30

24

20

120/7

a)What variation model does this table represent?

direct variation

inverse variation

 

b)What is the model that relates y and x?

y=720x

y=720x2

y=720/x

y=720/x2

Solution

As x increases, y is decreasing, so we know that the table represents an inverse variation model. In this case, the model is y=k/x (also, xy=k) where k is easily calculated using simple algebra. K=720; therefore, the model is y=720/x.