Terrence buys a new car for $20,000. The value of the car depreciates by 15% each year. If f(x) represents the value of the car after x years, which function represents the car’s value? f(x) = 20,000(0.85)x
f(x) = 20,000(0.15)x
f(x) = 20,000(1.15)x
f(x) = 20,000(1.85)x

In an experiment examining the effects tai chi on arthritis pain, callahan (2010) selected a large sample of individuals with doctor-diagnosed arthritis. half of the participants immediately began a tai chi course and the other half (the control group) waited 8 weeks before beginning. at the end of 8 weeks, the individuals who had experienced tai chi had less arthritis pain that those who had not participated in the course.