What are the independent, dependent, and controlled variables in Patty and Janice's skateboard experiment?

• They used two types of skateboards: four with 48-millimeter wheels and four with 60-millimeter wheels.
• All skateboards were ridden down the same ramp, which had a constant $30^\circ$ angle.
• They measured the time it took for each skateboard to go from top to bottom.

The experiment's independent variable is the wheel size, and the dependent variable is the time taken. The ramp angle ($30^\circ$) was a controlled variable.

Let's evaluate the given options:

• **Do skateboards with 60