Reverse percentages - PowerPoint presentation

This presentation has been successfully used to clarify to students the rationale behind and the method of calculating reverse percentages. The key point is to let students understand that if we add; say; 20% to an amount; going back to the original amount is NOT done by subtracting 20%; but rather by dividing the new amount by the multiplier (1.20 in tis example). Examples for calculating original amount both after percentage increase and decrease.