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We want to find the rate of change of the population of Austin, Texas in the years between 1980 and 1990.

The answer is: r = 12,600 people/year.

We will assume that this increase in population is modeled with a linear equation, remember that a general linear equation is:

y = a*x + b

Where the rate of change, or slope, is a.

We know that if a line passes through two points (x₁, y₁) and (x₂, y₂) the slope is given by the formula:

For this case we have two points, these are:

(1980, 346,000)

(1990, 472,000)

Then the slope or rate of change is just:

To be complete we need to add the correspondent units, which are people per year.

Then the rate of change is:

r = 12,600 people/year.

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