This video shows us the method to find the percent increase or decrease in a quantity. This can be done in 30 seconds. The formula states that the percentage increase or decrease is equal to the product of the ratio of amount (increase or decrease) and the original amount and 100. This is explained by two examples. In the first example the amount of increase of the price of groceries is found by taking the difference of the new price and the old price. This is divided by the original price and is multiplied by 100. In the second example the difference in the population is found by taking the difference of the old and new population. This is divided by the old population and the result is multiplied by 100.