What is a fair test?

• A. An experiment where only one variable is changed at a time and all other conditions are kept the same.
• B. An experiment with multiple variables changing at once.
• C. An experiment that uses no controls.
• D. An experiment that is done without any measurements.

Answer: (A)

A fair test means you change only one thing at a time and keep all other conditions the same. This lets you see whether the one thing you changed caused any difference in the results. For example, if you want to know whether sunlight helps a plant grow, you keep the plant type, soil, amount of water, pot, and environment the same for every plant, and only vary the amount of sunlight. If you change more than one factor at once, you can’t tell which change made any difference. Without controls or measurements, you wouldn’t be able to compare results reliably. So the best way is to change one variable at a time while keeping everything else the same.