Calculating Percent Decrease Step-by-Step

Math with Mr. J

A clear, step-by-step mathematics tutorial explaining how to calculate percent decrease. The video introduces the standard formula for finding percent of change: subtracting the old value from the new value to find the amount of change, dividing that difference by the original value, and multiplying by 100 to convert the decimal to a percentage. The instructor, Mr. J, demonstrates this process through two distinct examples involving integer values that result in decimal percentages. He explicitly addresses how to handle negative numbers in the numerator, explaining that the negative sign signifies a "decrease." He also shows two valid ways to express the final answer: as a negative percentage or as a positive percentage labeled with the word "decrease." This resource is highly valuable for middle school math classrooms covering ratios, proportions, and percentages. It specifically targets common student errors, such as dividing by the wrong number, by emphasizing the rule to "always divide by the old or original number." The procedural focus makes it an excellent tool for direct instruction, remediation, or homework support.