It looks like the 20% is 20% of the value that year, so it looks like value is shown with exponential decay. So if a car starts out at $20,000 it will be worth

It looks like the 20% is 20% of the value that year, so it looks like value is shown with exponential decay. So if a car starts out at $20,000 it will be worth $16,000 the next year, $12,800 after the second year, and $10,240 after the third. Notice that around the third year, the decrease in value slows considerably.