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May 2012

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(easy hangman)
(difficult)

The ideas in this geometry lesson are taken from Math Mammoth Early Geometry book.

Perimeter

The video below explains some of the ideas of this lesson.

Perimeter means the "walk-around", the distance you cover if you walk all the way around the figure.

Just think of jogging or running or hopping around the figure. Make a loop around the figure with your hand to show this!

The word comes from Greek word perimetros. In it, peri means 'around' and metros means 'measure'.

How many units is the perimeter?

To find the perimeter, just add all the side lengths. Often you need to figure out some side lengths that are not given.

Don't forget the unit of measurement in your answer. If the side lengths are in centimeters, the perimeter will be so-many centimeters. If the side lengths are "plain" numbers" without any particular unit, then the perimeter is so-many units.

What side lengths are not given?
The perimeter is _______ cm

1. Find the perimeter. Notice: some side lengths are not given! Remember to use
either “cm” or "in" or "units" in your answer.

[available in the book]

f.	[available in the book]

2. Find the perimeter....

a. of a square with sides 15 inches

b. [available in the book]

c. of a regular pentagon with 85 ft sides

To find the perimeter of this rectangle, count the units as you go around the figure.

The units are marked with arrows in the picture. The top side is four units long. The right side is two units long. Make sure you understand that!

So, what is the perimeter? _______ units

Here it is trickier to count
those little units. Be careful!

How many units is the perimeter?

3. Find the perimeter of these figures, in units.

P = units

[available in the book]

P = _________________

[available in the book]

P = _________________

[available in the book]

P = _________________

4. Let's not forget about the area. Find the area of the figures in problem #4.

a. A = _______ squares	b. A = _______ squares	c. A = _______ squares

d. A = _______ squares	e. A = _______ squares	f. A = _______ squares

5. a. The perimeter of a square is 24 cm. How long is the side of the square?

b. The perimeter of a square is 44 cm. How long is the side of the square?

c. [available in the book]

6. a. Draw a right triangle on a blank paper so that the two sides that are at a right
angle measure 5 cm and 12 cm, using these steps:

Draw a long line.

Mark two dots on the line that mark the side that is 12 cm.

Draw a line through one of the dots that is at a right angle with the first line. Use a protractor!

On the second line, measure and mark the 5-cm side.

Draw in the third side of the triangle now.

b. Find the perimeter of your triangle, in centimeters.

7. [available in the book]

8. a. A certain rectangle's perimeter is 30 cm, and its one side is 9 cm.
How long are the other sides?

b. [available in the book]

The ideas in this geometry lesson are taken from Math Mammoth Early Geometry book.