In this video, the instructor shows how to identify the percentage change using proportions. When a given quantity increases or decreases by certain amount then we can calculate the percentage change in the quantity, which can be either increase or decrease based on the new value of the quantity. To solve these kind of situations you should know that the ratio of amount of increase (or decrease) of an amount to its original amount is equal to the ratio of percentage increase (or decrease) to hundred. Now to compute the percentage increased or decreased substitute the old and new values in the above equation, which gives you the percentage, change in the quantity. This video shows how to compute the percentage increase or decrease of a value by using the proportions principle.