I Increased A Number 80% And Got 899. How Do I Calculate What The Original Number Was Obviously I Cannot Just Subtract 80% I Have 151 Numbers To Revert Back To Original From The 80% Increase ?

Let your original number be x, and your number after the increase be y.
x + 80%x = y
x(1 + 80%) = y
x = y/(1+80/100)
x = y/1.8

For your given problem,
x = 899/1.8 = 499.44
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If you would rather multiply, you can multiply by 1/1.8 = 5/9 ≈ .55556