6th Grade Math Textbook, Progress

Update your skills. See page 25.

Perimeter

13-8

Rita uses 54.6 m of fencing to enclose a play area for her

dogs. The play area is in the shape of a polygon, shown at

the right. She painted all but one side of the fence. How

many meters of fencing does Rita have left to paint?

To find how many meters of fencing left, x, write

and solve the equation:

sum of the lengths of sides is equal to perimeter

12.4 m
5.1 m
18.2 m
x  54.6 m

12.4
5.1
18.2
x54.6

35.7
x54.6 Simplify.

35.735.7
x54.635.7 Subtract 35.7 to isolate the variable.

x18.9 Simplify.

Rita has 18.9 m of fencing left to paint.

For some polygons, you can use formulas to find perimeter.

• Square or Rhombus P 4 s, where slength of side


• Rectangle P 2
  
  2 w or P2 (
  
  w),
  where
  length and wwidth


• Regular Polygon Pns, where nnumber of congruent sides,
  and slength of one side

P2 (

w) P 5 s

2 ( 1 yd
 yd) 5(4.1 cm)

4 yd 20.5 cm

To find the perimeter of a more complex figure, break it down into simpler figures

and then add the lengths of its actual sides.

P10 in.
(34 in.)
7 in.
(33 in.)

10 in.
12 in.
7 in.
9 in.

38 in.

5

6

1

6

Think

Add like units of measure.

Think

10  3  7

5.1 m

x

18.2 m

12.4 m

1 yd^16

(^56) yd
4.1 cm
3 in.
7 in.
10 in.
4 in.
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