Learn about Perimeter and its Applications In this lesson, let’s learn how to solve application problems that deal with perimeters. So we’ll do two problems. The first one says write the number that makes the equation true. The equation given to us is the perimeter is 10 + 4 + 4 + the missing number equals 28 centimeters. So we are given the perimeter is 28 centimeters. Well, what is the perimeter? Perimeter is the length of all the sides, length of all sides or the sum of the length of all sides. It’s the distance around the figure. So what would the perimeter of this rectangle be? It would be ten centimeters plus four centimeters plus 10 centimeters plus the missing side equals 28 centimeters. So we are given that these four sides when totaled equal 28 centimeters. Let’s total up the pre-sides that are given to us. 10 + 4, 14 + 4 is 24 centimeters plus some number gives us 28 centimeters. So what could that number be? What number when added to 24 gives 28? Well, that’s four, right. 24 + 4 = 28, so the missing number must be 4 centimeters. All we did was we looked at the equation and if all four these add up to 28 and three of them add up 24, well then the missing number must be four. Let’s do another problem on perimeter. It says that this picture shows Julia tablecloth. It is six feet one side, ten feet on the other side and then six and ten feet. It says the perimeter of Bill’s tablecloth is the same as perimeter of Julia’s but Bill is shaped like a square. So before we do this, let’s compute the perimeter of Julia’s tablecloth. What is it? Well, we start with the first side which is six feet plus the second side, ten feet, third side is six feet plus the fourth side is also ten feet. What do I have?—6, 16, 22, 32 feet. So the perimeter for Julia’s tablecloth is 32 feet that I have calculated, right. So now, let’s read the second part of the question. It says the perimeter of Bill’s tablecloth is the same as Julia’s. So perimeter of Bill’s tablecloth is 32 feet because it’s the same as Julia’s. But it is shaped like a square, so if we draw a square. What do we know about a square? All four sides are equal, right. So this side is S feet in length that this is also S, this is also S. This is also S. So 32 feet is the same as S + S + S + S, right. So which number when added four times give us 32? If I take 8 feet + 8 feet + 8 feet + 8 feet, if the length of one of the sides was 8 feet, we would get 32 feet. So that’s true. So what's the length of each side of Bill’s tablecloth? Well, the length that we are looking for must be 8 feet. We could have also said this is equaled 4 times S, right. We could have divided 32 by 4 and got an S as 8 feet but they’re both the same. Key thing to remember is a square has four equal sides. So the sum of all four sides has to be 32 feet which I can do in my head that each side is 8 feet because 8 added by itself, three more times gives us 32 feet.