In a three-variable graph with time on the x-axis, temperature on the y-axis, and production rate on the z-axis, which axis shows the dependent variable production rate?

• A. X-axis
• B. Y-axis
• C. Z-axis
• D. Legend axis

Answer: (C)

The key idea is that the dependent variable is the output you get from changing the inputs. Here, time and temperature are the inputs you can vary, so production rate is the result you’re observing. In a 3D plot, the output is placed on the third axis—the z-axis—so it shows how production rate changes as time and temperature change. The x-axis and y-axis represent the independent inputs (time and temperature), while the z-axis carries the dependent variable, production rate.