ACT Preparation / Unit 20 ACT 1913 short lesson, about 20 seconds
One Change at a Time
Captions available
The idea
A fair test changes one factor at a time. If two factors change together, any difference in the result cannot be assigned to either one.
In practice
Moving beans to blue light and a warmer room at once leaves the cause of faster growth unknown.
Where people slip
To test a second factor, run a separate trial in which only that factor changes.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Builds on
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