The graph below shows how the energy content of tomato ketchup compares with its weight .
How can you tell from the graph that varies directly as ?
The graph is a straight line through the origin therefore
Find the variation formula that connects and .
Therefore (where k is the constant of variation)
Choose any point on the graph, for example (, )
At that point and
Put these values into the equation
What is the energy content of grams of tomato ketchup?