PRACTICE: “Backwards” perimeter of rectangles
LEVEL 2
EXAMPLE: (common-sense way)
The perimeter of a rectangle is 18 in,
and its length is 6 in. What’s the
width? (HINT: Draw a diagram.)
EXAMPLE: (algebra way)
The perimeter of a rectangle is 18 in,
and its length is 6 in. What’s the
width? (HINT: Draw a diagram.)
6 in.
See diagram on left
?
?
P = 18
P = 2L + 2w
[from formula sheet]
18 = 2(6) + 2w
18 = 12 + 2w
6 in.
6 + 6 = 12 Since P = 18, there’s
18 – 12 = 6 left to be divided between
each side. The width is 3 in.
6 = 2w
w = 3 in.
YOUR TURN:
1) The perimeter of a rectangle is 34 ft, and its width is 2 ft.
What’s the length?
2) The perimeter of a rectangle is 13.8 m, and its length is 4.8 m.
What’s the width?
1
1
2
2
3) The perimeter of a rectangle is 17 in, and its length is 5 in.
Answers: 1) 15 ft
What’s the width?
D. Stark 4/29/2017
“Backwards” perimeter of rectangles
2) 2.1 m
4
3) 3 in
1