Calculating Area, Perimeter and Volume

Calculating Area, Perimeter and Volume

You will be given a formula table to complete your math assessment; however, we strongly recommend

that you memorize the following formulae which will be used regularly in your program.

Area of a square = s2

Area of a triangle = 1 b h or b h

2

2

Area of a rectangle = l w

Area of a parallelogram = b h

Area of a trapezoid = 1 h (a + b) 2

Area of a circle = r2

Volume of a cylinder = r2 h

Area of a cube = area of one face x number of faces

*NOTE* The symbol ? means multiply, so l w is the same as saying l x w

Area (Polygons)

A polygon is a geometric figure with 3 or more sides. The area of a polygon is the number of squares (of a particular unit) that it takes to cover the surface of the shape. Formulae are used to calculate the area.

Example 1: Find the area of a triangle which has a base of 10 mm and a height of 9 mm.

A= 1 bxh 2

A bxh 2

A = 1 (10 mm x 9 mm) 2

A 10 mm x 9 mm

or

2

A = 1 (90 mm2) 2

A = 45 mm2

A 90 mm2 2

A 45 mm2

Example 2: Find the area of a square that has a side with a length of 6 cm.

A = s2 A = (6 cm) 2 A = 36 cm2

Example 3: Find the area of a rectangle that has a length of 3.7 m and a width of 2.4 m. A= lxw

A = (3.7 m) x (2.4 m) A = 8.88 m2

Area, Perimeter and Volume ? Study Guide 5

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Example 4: Find the area of a parallelogram that has a base of 21 cm and a height of 13 cm. A = b x h A = (21 cm) x (13 cm) A = 273 cm2

*Notice that units in the answers are units2 (squared)

PRACTICE

Find the area of the following shapes:

a)

b)

c)

5 cm

10 cm

3 cm d)

5 cm

e)

f)

14 mm

24 mm g)

2.3 ft

11 cm

1 cm

h)

i)

10 ft

12 ft

4 ft

12.6 m

8.6 km

12.2 km

12.3 yd

Note: There are no diagrams for j) to q).

j) A square 35 ft on a side.

k) A parallelogram with height of 14 in. and base 23 in.

l) A rectangle with length of 8.8 m and width of 4.2 m.

m) A triangle with height of 9 km and base of 5.2 km.

n) A rectangle 3 mile by 7 mile.

4

8

o) A triangle with a base of 3 yard and height of 2 1 yd.

8

2

p) A parallelogram with base of 9 1 ft and height of 8 1 ft.

2

4

q) A trapezoid with one base of 6 m and one base of 4 m. The height is 8 m.

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* Tip* If you are asked to find the area of an unusual shape, break it down into shapes that you recognize. For example, if you were asked to find the area of the shape below, find the area of the triangle (roof) and then the house (rectangle). When you add the 2 areas together, you will have the total area.

a) 15 cm2

b) 25 cm2

ANSWERS

c) 158.76 m2

d) 336 mm2

e) 11 cm2

f) 52.46 km2

g) 5.29 ft2

h) 44 ft2

i) 151.29 yd2 j) 1225 ft2

k) 322 in2

l) 36.96 m2

o) 15 yd2 or 0.47 yd2

p)

32

m) 23.4 km2

n)

78 3 ft2 or 78.375 ft2 8

21 mi2 or 0.66 mi2 32

q) 40 m2

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Circle Geometry

Circumference is the name for the perimeter (or distance around the outside) of a circle. In this circle, the centre is Z. A, B, and C are points on the circle. Radius: The distance from the centre of the circle to any point on the circle is called the radius (r). (ZA is a radius. ZB and ZC are too). Diameter: The distance from any point on the circle, passing through the centrepoint and continuing on to the outer edge of the circle (d). (AB is the diameter of the circle to the right.)

To find the circumference (or perimeter) of the circle, use one of the following

formulae:

(1) C = d

OR

(2) C = 2 r

is called pi and is about 3.14 or 22

7

Example A: If the circle has a radius of 5 cm, then

(1)

C = d

(2)

C = 2 r

The diameter would be twice the radius

The radius is 5 cm

(or 5 cm x 2 = 10 cm)

So

C = (3.14) (10 cm)

C = (2) (3.14) (5)

C = 31.4 cm.

C = 31.4 cm

Both formulae work equally well. You may choose either one.

Now let's practice:

1. A circle has a diameter of 20 m. What is the circumference? 2. A circle has a radius of 7 km. What is the circumference? 3. Find the circumference for the following circles:

a) radius(r) = 14 cm b) diameter (d) = 60 mm c) radius (r) = 15 m (use = 3.14 or 22 ) 7

ANSWERS - Please note that answers may vary depending on the value used for (Pi)

1) C = d ; C = (3.14)(20); C = 62.8 m

2) C = 2 r; C = (2)(3.14)(7); C = 43.96 km

3) a) C = 2 r; C = (2) 22 (14) = 88 cm 7

b) C = d ; C = 3.14(60) = 188.4 mm

c) C = 2 r ; C = (2)(3.14)(15); C = 94.2 m

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Area (Circles)

To find the area of a circle, use the formula A = r 2 A = area of the circle: = pi 3.14 or 22

7 r = the radius of the circle

r = the radius of the circle = 10 cm

so

A = r 2 A = 3.14 x (10)2 A = 3.14 x 100 A = 314 cm2

*notice: answers are units2

Now let's practice:

A: Find the circumference and the area of the following circles:

(1) the radius = 4 km

(2) the diameter = 10 m

B: Find the circumference and the area of the following circles:

(1) the radius = 14 in.

(2) the diameter = 20 mm

ANSWERS - - Please note that answers may vary depending on the value used for (Pi)

A: 1) C = 2 r; C = 2 (3.14)(4): C = 25.12 km

A = r 2 A = (3.14)( 4)2 = 50.24 km2

2) C= d ; C = (3.14)(10); C = 31.4m

A = r 2 A = (3.14)(5)2 = 78.5 m2

B: 3) C = 2 r; C = 2( 3.14)( 14) = 87.92 in

A = r2 A = (3.14)(14)2 = 615.44 in 2

4) C= d ; C = (3.14)(20) = 62.8 mm

A = r 2 A = (3.14)(10)2 = 314 mm 2

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