Perimeter - a lesson with video and varied exercises

This third grade geometry lesson explains the concept of perimeter and has varied exercises for students. The included video explains some of the same ideas.

Perimeter means the “walk-around measure,” or the distance you go if you walk all
the way around the figure.

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

To find the perimeter of this rectangle, count the units as you go
around the figure. You can think of running or hopping around
the figure.

The units are marked with little 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? _______ units

1. Find the perimeter of these figures. Your answer will be so many units. P means perimeter.

a.
P = units

b.
P = _______________

c.
P = _______________

d.
P = _______________

e.
P = _______________

f.
P = _______________

2. Measure with a ruler to find the perimeter of these figures in centimeters.

a.
P = ____________ cm

b.
P = ____________ cm

To find the perimeter, simply
add all the side lengths.

How many units is the perimeter
of the triangle on the right?

It is 8 + 9 + 10 units, or _______ units.

Often you need to figure out some
side lengths that are not given.

What side lengths are not given?

The perimeter is _______ cm.

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.

4. Find the perimeter. Notice: some side lengths are not given! Don't forget to use either “cm”
or “in.” or “units” in your answer.

P = units

P = ________________

5. Find the perimeter....

a. ...of a square with 7-in. sides

b. ...of a square with 13-cm sides

Math Mammoth Early Geometry

A self-teaching worktext for 1st - 3rd grade that covers basic shapes, right angle, symmetry, area, perimeter, and solids.

Download ($5.95). Also available as a printed copy.

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