Answer:
15% decrease
Step-by-step explanation:
The appropriate formula is ...
(percentage change) = (amount of change)/(original value) × 100%
Where the amount of change is ...
(amount of change) = (new value) - (original value)
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Putting these two formulas together, we get ...
(percentage change) = ((new value) - (original value))/(original value) × 100%
__
Another way to write the same formula is ...
(percentage change) = ((new value)/(original value) - 1) × 100%
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Filling in the numbers you have, you get ...
(percentage change) = (17 - 20)/20 × 100%
= -3/20 × 100%
= -15%
When the percentage change is <em>negative</em>, it means the change was a <em>decrease</em>.
Here, you know the change is a decrease and you just want to know the amount of decrease. That amount is a 15% decrease.
