ACT Preparation / Unit 7 ACT 0632 short lesson, about 20 seconds
Successive Percent Changes Do Not Add
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The idea
Two percent changes in a row multiply; they do not add. Up p then down p multiplies the amount by 1 − p², less than the start.
In practice
Up 20% then down 20%: 1.2 × 0.8 = 0.96, a 4% loss, not zero change.
Where people slip
The second percent is taken of a new base, so the changes cannot be added.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Unlocks
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