Change one thing at a time
Two pots hold the same kind of plant. Pot B gets more water, more light and richer soil. Richer soil gives plants more of what they take from soil.
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Step 1 of 4
- Two pots. Three things you could change.
- Only water is different between them.
- One thing differs, so water is the cause.
- Change light and soil too. Now no one cause is clear.
Fair test — a test that changes only one thing. Everything else stays the same.
The cause is the change that made the result.
Only the water differs, and Pot B grows taller. Then only water can explain the difference.
Water, light and soil all differ, and Pot B grows taller. You cannot say which change helped.