Video: Finding the Perimeter of a Rectangle given Its Dimensions

Find the perimeter of the rectangle.

02:33

Video Transcript

Find the perimeter of the rectangle.

First of all, what does perimeter mean? The perimeter is the distance all the way around an object. We find the perimeter by adding up all the sides. To find the perimeter of a rectangle, we could add its four sides: side one plus side two plus side three plus side four. Or when we’re working with rectangles, we can multiply two times the length plus the width.

Let’s talk about why. If the length is 15 centimeters and the width is 10 centimeters, the side across from the 15-centimeter length is also a length of 15 centimeters. The side across from the width of 10 centimeters is another width of 10 centimeters.

Let’s then put our two different formulas side by side and solve them. The first version for solving the perimeter is to add up all four sides. We can start at the top. 15 plus 10 plus 15 plus 10 equals the perimeter. Now let’s fill in our second equation. The perimeter equals two times the length 15 plus the width of 10.

For the first formula, we can add up 15 and 10 plus 15 plus 10. Five plus zero plus five plus zero equals 10. We write down our zero and carry our one. One plus one plus one plus one plus one equals five. Our first formula tells us that the perimeter is 50 centimeters.

Let’s try the second option. 15 plus 10 is in parentheses. So we do that first. 15 plus 10 is 25. Two times 25 equals 50. Both formulas give us an outcome of 50 centimeters. The perimeter, the distance all the way around this rectangle, is 50 centimeters.

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