9-4 Direct Variation

9-4 Direct Variation

Chapter 9 Lesson 4

What is direct variation?

When the ratio of two variable quantities is constant, their relationship is a direct variation.

A direct variation is considered a PROPORTIONAL RELATIONSHIP!

The equation is y = mx, where "m" is the constant of variation!

Multiple Choice

Given the graph, determine if the relationship between the cost and the weight of the trail mix is a direct variation. If it is, find the equation of the line.

• Yes, it is. The equation is y = 3.50x

• Yes, it is. The equation is y = 7x.

• No, this is not a direct variation.

Open Ended

The equation y = 40x represents the distance y in miles an ostrich can travel in x hours. Determine whether there is a constant of variation. If so, explain what it represents in this situation.

Multiple Choice

The time it takes to burn amounts of information on a CD varies directly with the amount of information. Write and solve an equatin to find how long it will take to fill a 700-megabyte CD.

• Equation: y = 0.25x

  Answer: 175 seconds

• Equation: y = 4x

  Answer: 2800 seconds

• Equation: y = 25x

  Answer: 17,500 seconds

Open Ended

The equation y = 1.5x represents the relationship between the number of heartbeats y and time in seconds x for a dog. The graph shows the heartbeats for a cat. Which animal has a faster heart rate? How do you know?