# 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
 c. 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”

 a. 6 P =          units

 b. P = ________________

 c. P = ________________

5. Find the perimeter....

a.  ...of a square with 7-in. sides

b.  ...of a square with 13-cm sides

This lesson is taken from Maria Miller's book Math Mammoth Early Geometry, and posted at www.HomeschoolMath.net with permission from the author. Copyright © Maria Miller.

#### Math Mammoth Early Geometry

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