1. Algebra 1 Section 4.5 Solve direct variation problems
The cost of filling up your gas tank depends upon the number of gallons of gasoline that you buy.
As the number of gallons bought increases, so does the total cost. This is an example of a direct variation.
Number of gallons
Cost in $ 1
2.25 2
4.50 3
6.75 4
9.00
Direct Variation Equation
y varies directly as x
y = kx
k is the constant of variation

2. Cost – gallons problem
The graph of a direct variation is a line that passes through the origin and it has a slope of k.
C = 2.25 g

3. example
y varies directly as x. If y = 15 when x = 3, find: A. The equation relating x and y. B. The value of y when x = 7

4. Example 3 page 235
Page 237
Problems even, 33,44,58