Notes with answers - Summit Schools

Your Notes
Homework
Example 3 Identify Direct Variation
The table gives sample cell phone bills, showing the
total monthly cost and the number of minutes used
per month. Tell whether total cost and the number of
minutes show direct variation. If so, write an equation
relating c and m.
Total cost, c (dollars) 35 45 80 15 28
Minutes used, m 100 129 229 43 80
solution
Find the ratio of c to m for each data pair.
35
}
100
15
}
43
5 0.35 45
}
129
28
< 0.35 } 5 0.35
30
Checkpoint Complete the following exercise.
3. Tell whether the data (21, 22), (1, 2), (3, 6),
(5, 10), (7, 14) show direct variation. If so, write an
expression relating x and y.
direct variation; y 5 2x
80
< 0.35 } < 0.35
229
The ratio of c to m in each pair is nearly the same , so
the data show direct variation . Substituting 0.35
for k in c 5 km gives the direct variation equation
c 5 0.35 m, which relates the total cost to number of
minutes used.
42 Lesson 2.6 • Algebra 2 C&S Notetaking Guide Copyright © McDougal Littell/Houghton Mifflin Company