How to Calculate the Slope of a Demand Curve With a Table


The demand curve is a graph used in economics to demonstrate the relationship between the price of a product and the demand for that same product. The graph is calculated using a linear function that is defined as P = a - bQ, where "P" equals the price of the product, "Q" equals the quantity demanded of the product, and "a" is equivalent to non-price factors that affect the demand of the product. Given a table, it is simple to solve for the slope of a demand curve at a point using the linear demand curve equation or the equation for the slope of a linear equation.

Solving for Slope with Linear Demand Curve Table

Find Values From Data

Write down a set of values for a certain point on the graph from the data provided within the table. For example, if the table states that at point (30, 2) the value of Q = 30, the value of P = 2 and the value of a = 4, write them out on a piece of paper for easy access.

Insert Values Into Equation

Insert the values into the linear demand curve equation, Q = a - bP. For example, using the above values found from the example table, insert Q = 30, P = 2 and a = 4 into the equation: 30 = 4 - 2b.

Isolate b Variable

Isolate the b variable on one side of the equation in order to solve for the slope. For example, using algebra we find: 30 = 4 - 2b becomes 30 - 4 = - 2b, becomes -26 = 2b, becomes -26 ÷ 2 = b.

Solve for the Slope

Solve for the slope "b" using your calculator or by hand. For example, solving the equation -26 ÷ 2 = b finds b = -13. So, the slope for this set of parameters equals -13.

Using Slope-Intercept Form with a Coordinate Table

Find Values From Table

Write down the x and y values from two points listed on a demand curve's coordinate table. In the case of a demand curve, the point "x" equals the quantity demanded of a product and the point "y" equals the price of the product at that level of demand.

Insert Values Into Equation

Insert these values into the slope equation: slope = change in y / change in x. For example, if the table states that the values of of x1 = 3, x2 = 5, y1 = 2 and y2 = 3, the slope equation is set up like this: slope = (3 - 5) ÷ (2 - 3).

Solve Slope Equation

Solve the slope equation to find the slope of the demand curve between the two chosen points. For example, if the slope = (3 - 5) ÷ (2 - 3), then slope = -2 ÷ -1 = 2.


About the Author

Luc Braybury began writing professionally in 2010. He specializes in science and technology writing and has published on various websites. He received his Bachelor of Science in applied physics from Armstrong Atlantic State University in Savannah, Ga.