↑ 128 is 20% of 640 Lets solve: 640 IS 100% Because its the output value of the task So lets look for x We got 100%=640 and x%=128 Now im going to write this out as 100% / x%=640/128 Now we just have to solve this simple equation. (100/x)*x=(640/128)*x -Multiply both sides of the equation by x Now we divide both sides of the equation by 5 to get x. 100=5x 100/5=x 20=x and x=20 So we got our answer of 20%