Question

In 2000, people charged 1,243 billion on the four most used types of credit cards. In 2005, people charged 1,838 billion on these same four types of credit cards. What was the rate of change?

Answer 1

Alright, so the rate of change is the same thing as the slope, so we can find this by using the slope formula (which I took a picture of because it's super messy to type it out like this)

Now that we know the slope formula, we need to find the x values and the y values to plug into the equation. We'll say that the years are our x values and the money spent (in billions) are our y values. Now that we've set up an axis, we can create points! Our points would be (2000, 1243) and (2005, 1838)

Now we can plug our points into our equations! On the top of our equation, we'll put (1838-1243), and on the bottom we'll put (2005-2000). When we simplify that, we end up with 595/5, which simplifies to 119. Now we know that the rate of change for the credit cards was 119 billion!