In this lesson we're going to learn about percent change. We'll see how a value can increase or decrease to another value. And then we'll calculate how much it changed in terms of a percent. Here's our first example. The number of students in Hillside Middle School increased from 425 to 503 since last year. Find the increase of students as a percentage. So the first thing that we need to do is find what the difference is as a number. So we'll look at the problem and compare the two numbers that we have for the 425 students for last year and the 503 students for this year. So we'll find that difference by subtracting them.  503-425 equals 78 so the number of students increased by 78. But the problem tells us to find that increase as a percent. So now we're going to take that difference, the 78 students, and divide it by the original number of students, which is the number of students that we had the last year. So we're going to take 78 and divide it by the 425 students that there were the last year. And now that gives us zero point 184 or 184 thousandths. Now we can take that decimal and make it look a little more like a percent. So we'll multiply it by 100, which gives us 18.4 and then add the percent sign. And that's our final answer. So we can say that the number of students increased by 18.4%. Here's one more example. The price for a gallon of gas is now $2.85. Find the percent change if it was $2.97 last week. So just like before, we need to find the difference as a number. So we'll take a look at those two gas prices. It's now $2.85, but it was $2.97 last week, so the price actually went down. So we'll subtract those two amounts. $2.97 minus $2.85 means that the price went down by twelve cents. And now we need to calculate that as a percent. So we'll take the divide it by the original price, the price that it was before, which was $2.97. So we have $0.12, divide it by $2.97, which gives us point zero four or 400ths, and then we'll change that into a percentage. So we'll multiply it by 100, which gives us four, and then add the percent sign so we can say that the price of gas decreased by 4%. And now we can take all of those steps that we just did to calculate the percent increase or decrease. And we can organize them all together in a formula. So for each of those problems, the first thing that we had to do was find the difference in the two values. And then we divided it by the original value. Once we calculated that, we multiplied that answer by 100 and added a percent sign to change it into a percent. So if you follow those steps, you'll be able to calculate percent change for any word problem.