working backward is fair game

Work backward from area to find butt-space

Normally, you’re given the lengths of the sides of a shape and you

push them through a couple of formulas to get area and perimeter:

Side

length

Perimeter

Start

Area

formula

Perimeter

formula

Area

Usuall

y this is

wha

t y

ou’r

e given.

Often you’r

e aiming

f

or one of these.

But in this case, you know your hot tub area, and you need to find

the length of the sides that would give that area, so you can use

them to find the perimeter (butt-space). To do this you need to work

backward.

Side

length

Perimeter

Start

Area

formula

Perimeter

formula

Area

W

e know the area

of our hot tub.

W

e need t

o find the

side length firs

t.

T

his is our goa

l.

284 Chapter 7

regular polygons

Use any formula you know for area of a square to find the side lengths of the square hot

tub with 6 square meters area.

Then use the side length to find the perimeter.

If each butt requires 0.5 meters of perimeter, how many butts fit in this square hot tub?

6m

2

Reviewing isn’t cheating! Quads

area formulas: page 272.

you are here 4 285

exercise solution

286 Chapter 7

Area of a square = side length x side length

If you had width x height

that w

orks t

oo—but in a

squar

e the width and height

ar

e the same so i

t’s ev

en easi

er!

Perimeter of a square = 4s

Perimeter = 4 x 2.45 = 9.8 meters

Each butt takes 0.5 meters

total butts = 9.8 = 19.6 butts

0.5

2.45 meters = s

6 = s

6 = s

2

Length of

each side.

Uni

ts help y

ou keep

track of wha

t each

Use any formula you know for area of a square to find the side lengths of the square hot

tub with 6 square meters area.

Then use the side length to find the perimeter.

If each butt requires 0.5 meters of perimeter, how many butts fit in this square hot tub?

6m

2

number means.

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