To decrease by 20% is to be multiplied by 100%-20% or 80% or multiplied by 0.80: 1000×0.80 = 800 800×0.80 = 640 640×0.80 = 512 512×0.80 = 409.6 409.6×0.80 = 327.68 327.68×0.80 = 262.144 262.144×0.80 = 209.7152 Edwin