Percent of decrease
Just like the name suggests, the percent of decrease is the amount of decrease out of one hundred. Once we know what the decrease is, just divide the decrease by the original amount and express the answer as a percent. The formula along with a nice example are shown in the figure below.
The amount of decrease is the original amount minus the final amount. For example if you are looking for the percent of decrease from 9 to 6, the original amount is 9 and the final amount is 6.
Then, as you can see in the formula below, you need to do the followings:
 1. Divide the amount of decrease by the original amount.
 2. Multiply the answer you found in step 1 by 100.
 3. Put the percent sign (%) next to the answer you found in step 2.
A few more carefully chosen examples showing how to find the percent of decrease.
Example #1:
Find the percent of decrease from 6 to 4.
Amount of decrease is 6 − 4 = 2.
Original amount is 6.
2 / 6 = 0.3333
Multiply 0.3333 by one hundred and put the percent sign next to it to get the answer as a percent.
0.3333 × 100 = 33.33, so the answer is 33.333333%.
Check
6 × 33.33% = 6 × 0.333333 = 2
6  2 is indeed equal to 4.
Example #2:
Find the amount of decrease per hundred from 10 to 5.
Amount of decrease is 10 − 5 = 5.
Original amount is 10.
5 / 10 = 0.50
Multiply 0.50 by one hundred and put the percent sign next to it to get the answer as a percent.
0.50 × 100 = 50, so the answer is 50%.
Check
10 × 50% = 10 × 0.50 = 5
10  5 is indeed equal to 5.
Example #3
Find the amount of decrease per hundred from 4 to 8.
Amount of decrease is 4 − 8 = 4 + 8 = 4
Original amount is 4
4 / 4 = 1
Multiply 1 by one hundred and put the percent sign next to it to get the answer as a percent.
1 × 100 = 100, so the answer is 100%.
Check
4 × 100% = 4 × 1 = 4
4  4 is indeed equal to 8.

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