Hello everybody!!! I need help with understanding how to find percent change.

My book gives this formula:(amount of change/original amount) * 100%

For a problem that looks like this:80 to 100, I usually just do 20/80, which is equal to 25% (which my book's answer key tells me I am correct)

Soooo.

For a problem that reads 200 to 100, would you do 100/200, or -100/200??

And one more thing:

The formula our book tells us to use says to multiply the amount of change divided by the original amount by 100% (1.00).

What is the point of multiplying by one??

Thank you guys!!!

All help will be greatly appreciated!!!

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