A percentage change acts on a named base. When a second change acts on the new amount, that base has moved. This lesson shows how to keep track of the movement, undo a known sequence, compare quantities in the reverse direction, and describe a change in a percentage rate precisely. You should already be able to convert a percentage to a decimal, find a part of a positive whole and solve a simple equation. First check: 12% = 0.12, and retaining 88% means multiplying by 0.88.