Answer: 20%
Step-by-step explanation:
If we let the original amount be x, then after increasing it by 25%, we now have 1.25x
To get this back to x, we need to do 1.25x*(something) = x
this gives us that something = 1/1.25 = 0.8
meaning you need to decrease it by 100% - 80% = 20%
