That would be a 30% Decrease.
Here is how I found the answer:
Step 1: Find the difference between the two numbers by using this formula: Original Number - New number = Decrease.
Step 2: Divide the decrease by the original number and then multiply your answer by 100 by using this formula: Decrease / Original Number = % Decrease.
Now you can use these formulas to find any percentage decrease between two numbers.