How to find the perimeter of a rectangle

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ACT Math › How to find the perimeter of a rectangle

Questions 1 - 10
1

What is the perimeter of the below rectangle in simplest radical form?

Act_math_159_15

4√3 + 2√27

5√3

10√3

7√27

Explanation

The perimeter of a figure is the sum of the lengths of all of its sides. The perimeter of this figure is √27 + 2√3 + √27 + 2√3. But, √27 = √9√3 = 3√3 . Now all of the sides have the same number underneath of the radical symbol (i.e. the same radicand) and so the coefficients of each radical can be added together. The result is that the perimeter is equal to 10√3.

2

Find the perimeter of a perimeter with width 5 and length 9.

Explanation

To solve, simply use the formula for the perimeter of a rectangle. Thus,

3

A rectangle has an area of 56 square feet, and a width of 4 feet. What is the perimeter, in feet, of the rectangle?

14

28

30

36

120

Explanation

Divide the area of the rectangle by the width in order to find the length of 14 feet. The perimeter is the sum of the side lengths, which in this case is 14 feet + 4 feet +14 feet + 4 feet, or 36 feet.

4

The area of a rectangle is , and the width of this rectangle is two times its height. What is the perimeter of the rectangle?

Explanation

The area of a rectangle is the width times the height, and we are told that in this rectangle the width is two times the height.

Therefore, .

Plug in the value of the area:

Solve for to find a width of 4 inches. Using our formula above, the height must be 8 inches. We then add all the sides of the rectangle together to find the perimeter:

5

Robert is designing a rectangular garden. He wants the area of the garden to be 9 square meters. If the length of the lot is going to be three meters less than twice the width, what will the perimeter of the lot be in meters?

1.5

3

6

12

10

Explanation

Let l be the length of the garden and w be the width.

By the specifications of the problem, l = 2w-3.

Plug this in for length in the area formula:

A = l x w = (2w - 3) x w = 9

Solve for the width:

2w²- 3w - 9 =0

(2w + 3)(w - 3) = 0

w is either 3 or -3/2, but we can't have a negative width, so w = 3.

If w = 3, then length = 2(3) - 3 = 3.

Now plug the width and length into the formula for perimeter:

P = 2 l + 2w = 2(3) + 2(3) = 12

6

The area of a yard is . If one side is in length, how many feet of fence would be needed to surround the yard?

Explanation

Begin by computing the length of the other side of the yard. Based on the data that you have, you know that:

, where is the other side in yards. Solving for is:

Now, this means that our yard's dimensions in feet are:

The perimeter will be . For our data, this is:

7

What is the perimeter of a rectangle with one side of and an area of ?

Explanation

Based on the information provided, you know that the rectangle's area could be represented as:

, where is the unknown side of the rectangle. Solving for , you get .

Now, remember that your perimeter is just the sum of all the sides. This is:

For our data, this is:

8

A rectangle has an area of and one side has a length of , what is the perimeter of the rectangle?

Explanation

To find the length and width of a rectangle given the area and one side, simply divide the area by the given side length:

Next, to find the perimeter use the formula:

9

Find the perimeter of a perimeter with width 5 and length 8.

Explanation

To solve, simply use the formula for the perimeter of a rectangle. Thus,

10

Kayla took 25 minutes to walk around a rectangular city block. If the block's width is 1/4 the size of the length, how long would it take to walk along one length?

10 minutes

7 minutes

2.5 minutes

8 minutes

Explanation

Leaving the width to be x, the length is 4_x_. The total perimeter is 4_x_ + 4_x_ + x + x = 10x.

We divide 25 by 10 to get 2.5, the time required to walk the width. Therefore the time required to walk the length is (4)(2.5) = 10.

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