ISEE Middle Level Math : Plane Geometry

Study concepts, example questions & explanations for ISEE Middle Level Math

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Example Questions

Example Question #12 : How To Find The Perimeter Of The Rectangle

The length of a rectangle is 1 cm more than 3 times the width.  What is the perimeter of the rectangle if the width is 32 cm?

Possible Answers:

\displaystyle 194cm

\displaystyle 258cm

\displaystyle 64cm

\displaystyle 97 cm

Correct answer:

\displaystyle 258cm

Explanation:

First find the length.

length or \displaystyle l=3w + 1

\displaystyle (3 \times 32) + 1 = 97

The length is \displaystyle 97cm

Find the perimeter.

\displaystyle P = 2l + 2w

\displaystyle P = 2(97) + 2(32)

\displaystyle P = 194 + 64

\displaystyle P = 258

The perimeter is \displaystyle 258cm when the width is \displaystyle 32cm.

Example Question #13 : How To Find The Perimeter Of The Rectangle

Use the following to answer the question.

Rectangle4

Find the perimeter of the rectangle if the width is half the length.

Possible Answers:

\displaystyle 72\text{ft}

\displaystyle \text{There is not enough information to answer the question.}

\displaystyle 36\text{ft}

\displaystyle 72\text{ft}^2

\displaystyle 36\text{ft}^2

Correct answer:

\displaystyle 36\text{ft}

Explanation:

To find the perimeter of a rectangle, we use the following formula:

\displaystyle \text{perimeter of rectangle} = a+b+c+d

where a, b, c, and d are the lengths of the sides of the rectangle.

 

Now, in the rectangle

Rectangle4

we can see the length is 12 feet.  Because it is a rectangle, we know the opposite side is also 12 feet.  We know the width is half of the length.  So, the width is 6 feet.  Because it is a rectangle, the opposite side is also 6 feet.  Knowing this, we can substitute into the formula.  We get

\displaystyle \text{perimeter of rectangle} = 12\text{ft} + 12\text{ft} + 6\text{ft} + 6\text{ft}

\displaystyle \text{perimeter of rectangle} = 36\text{ft}

Example Question #231 : Plane Geometry

The Smartboard in your math classroom is 3 feet tall and 20 feet long. What is the perimeter of the Smartboard?

 

Possible Answers:

\displaystyle 23 ft

\displaystyle 60ft

\displaystyle 120ft

\displaystyle 46ft

Correct answer:

\displaystyle 46ft

Explanation:

The Smartboard in your math classroom is 3 feet tall and 20 feet long. What is the perimeter of the Smartboard?

 

We need to find the perimeter of the rectangle that is the Smartboard.

To do so, we simply add up the sides. In this case, we have 2 3ft sides and 2 20 ft sides.

\displaystyle P=3+3+20+20=46

So our answer is 46

Example Question #232 : Plane Geometry

Find the distance around a rug if the rug is 2 feet wide and its length is 3 times the width.

Possible Answers:

\displaystyle 24ft

\displaystyle 12ft

\displaystyle 36ft

\displaystyle 16ft

Correct answer:

\displaystyle 16ft

Explanation:

Find the distance around a rectangular rug if the rug is 2 feet wide and its length is 3 times the width.

We are really being asked to find the perimeter. To do so, we first need to dimensions.

We are told the width is two feet.

The length is three times the width. \displaystyle 2ft*3=6ft

Now, use the following to find the perimeter:

\displaystyle p_{rectangle}=2l+2w=2(6ft)+2(2ft)=12ft+4ft=16ft

So our answer is 16 feet

 

 

Example Question #16 : How To Find The Perimeter Of The Rectangle

Rectangles 1

Refer to the above figures. The square at left has perimeter 160. Give the perimeter of the rectangle at right.

Possible Answers:

\displaystyle 200

\displaystyle 240

\displaystyle 160

\displaystyle 128

Correct answer:

\displaystyle 200

Explanation:

The perimeter of a square is four times the length of a side - here, this is \displaystyle 4x.

The perimeter of a rectangle is twice the sum of its length and its width - here, this is \displaystyle 2 \left ( \frac{1}{2} x + 2x \right ) = 2 \left ( 2\frac{1}{2} x \right ) = 5x.

The square has perimeter 160, so

\displaystyle 4x = 160

\displaystyle 4x \div 4 = 160 \div 4

\displaystyle x = 40

The perimeter of the rectangle is \displaystyle 5x = 5 (40 ) = 200.

Example Question #233 : Plane Geometry

A rectangular postage stamp has a width of 3 cm and a height of 12 cm. Find the perimeter of the stamp.

Possible Answers:

\displaystyle 15cm

\displaystyle 36cm

\displaystyle 30cm

\displaystyle 30cm^2

Correct answer:

\displaystyle 30cm

Explanation:

A rectangular postage stamp has a width of 3 cm and a height of 12 cm. Find the perimeter of the stamp.

To find the perimeter of a rectangle (or any shape) simply add up all the sides.

In this case, we have two sides that are 3 cm and two sides that are 12 cm.

\displaystyle P=3cm+3cm+12cm+12cm=30cm

Now, our answer must be in centimeters and not centimeters squared, because we are dealing with perimeter, which is a measure of length.

Example Question #18 : How To Find The Perimeter Of The Rectangle

Find the perimeter of a rectangle with a width of 6 cm and a length that is two times the width.

Possible Answers:

\displaystyle 72\text{cm}^2

\displaystyle 36\text{cm}^2

\displaystyle 36\text{cm}

\displaystyle 72\text{cm}

\displaystyle 18\text{cm}

Correct answer:

\displaystyle 36\text{cm}

Explanation:

To find the perimeter of a rectangle, we will use the following formula:

\displaystyle \text{perimeter of rectangle} = a+b+c+d

where a, b, c, and d are the lengths of the sides of the rectangle.

 

Now, we know the width of the rectangle is 6cm.  Because it is a rectangle, we know the opposite side is equal.  Therefore, the opposite side is also 6cm.  

We also know the length is two times the width.  Therefore, the length is 12cm.  Because it is a rectangle, we know the opposite side is equal.  Therefore, the opposite side is also 12cm.

Knowing this, we can substitute into the formula.  We get

\displaystyle \text{perimeter of rectangle} = 6\text{cm} + 6\text{cm} + 12\text{cm} + 12\text{cm}

\displaystyle \text{perimeter of rectangle} = 36\text{cm}

Example Question #21 : How To Find The Perimeter Of The Rectangle

Find the perimeter of a rectangle with a length of 8cm and a width that is half the length.

Possible Answers:

\displaystyle \text{There is not enough information to solve the problem.}

\displaystyle 24\text{cm}

\displaystyle 32\text{cm}

\displaystyle 24\text{cm}^2

\displaystyle 32\text{cm}^2

Correct answer:

\displaystyle 24\text{cm}

Explanation:

To find the perimeter of a rectangle, we will use the following formula:

\displaystyle \text{perimeter of rectangle} = a+b+c+d

where a, b, c, and d are the lengths of the sides of the rectangle.

 

Now, we know the length of the rectangle is 8cm.  Because it is a rectangle, we know the opposite side is also 8cm.  We also know the width is half the length.  Therefore, the width of the rectangle is 4cm.  Because it is a rectangle, we know the opposite side is also 4cm.  Knowing this, we can substitute into the formula.  We get

\displaystyle \text{perimeter of rectangle} = 8\text{cm} + 8\text{cm} + 4\text{cm} + 4\text{cm}

\displaystyle \text{perimeter of rectangle} = 24\text{cm}

Example Question #22 : How To Find The Perimeter Of The Rectangle

Find the perimeter of a rectangle with a width of 4in and a length that is 3 times the width.

Possible Answers:

\displaystyle 32\text{in}

\displaystyle 7\text{in}

\displaystyle 12\text{in}

\displaystyle 17\text{in}

\displaystyle 48\text{in}

Correct answer:

\displaystyle 32\text{in}

Explanation:

To find the perimeter of a rectangle, we will use the following formula:

\displaystyle \text{perimeter of rectangle} = a+b+c+d

where a, b, c, and d are the lengths of the sides of the rectangle.

 

Now, we know the width of the rectangle is 4in.  Because it is a rectangle, we know the opposite side is also 4in.  

We know the length is 3 times the width.  Therefore, the length is 12in.  Because it is a rectangle, we know the opposite side is also 12in.  

Knowing all of this, we can substitute into the formula.  We get

\displaystyle \text{perimeter of rectangle} = 4\text{in} + 4\text{in} + 12\text{in} + 12\text{in}

\displaystyle \text{perimeter of rectangle} = 32\text{in}

Example Question #23 : How To Find The Perimeter Of The Rectangle

Find the perimeter of a rectangle with a width of 8cm and a length that is three times the width.

Possible Answers:

\displaystyle 64\text{cm}

\displaystyle 32\text{cm}

\displaystyle 22\text{cm}

\displaystyle 56\text{cm}

\displaystyle 24\text{cm}

Correct answer:

\displaystyle 64\text{cm}

Explanation:

To find the perimeter of a rectangle, we will use the following formula:

\displaystyle \text{perimeter of rectangle} =a+b+c+d

where a, b, c, and d are the lengths of the sides of the rectangle.

 

Now, we know the width of the rectangle is 8cm.  Because it is a rectangle, we know the opposite side is also 8cm.  We also know the length is three times the width.  Therefore, the length is 24cm.  Because it is a rectangle, we know the opposite side is also 24cm.  

Knowing all of this, we can substitute into the formula.  We get

\displaystyle \text{perimeter of rectangle} = 8\text{cm} + 8\text{cm} +24\text{cm} + 24\text{cm}

\displaystyle \text{perimeter of rectangle} = 64\text{cm}

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