Calculating Area of Circle

Area of Circle

(Real World Examples)

Async Wednesday Jan 13, 2021

Area of a Circle

• How much space a circle covers

• Real World Applications: How much grass seed would be needed to cover a circular yard, how much fertilizer is needed to cover a circular garden, the amount of frosting needed to cover a cookie, how big of a table cloth to cover a circular table, how big of a rug to cover a circular floor

•  $Area=\ \pi\ r^2$   $Area\ =\ \pi\ \times\ r\ \times\ r\$  

•  $Area\ =\ 3.14\ \times\ r\ \times\ r$  

Find the Area

 $Area\ =\ \pi\ r^2$  
 $\pi\ \approx3.14$  
 $Radius\ \left(r\right)\ =\ 8m$  

 $Area\ =\ 3.14\ \times8\times8$  

 $Area\ =\ 200.96\ sq\ m^{ }$  

Find the Area

•  $Area\ =\ \pi\ r^2$  

•  $\pi\approx3.14$  

•  $Radius\ \left(r\right)\ =\ 10m$  

•  $Area\ =\ 3.14\times10\times10$  

•  $Area\ =\ 314\ sq\ m$  

Multiple Choice

What is the area of this circle?

• 62.59 cm²

• 113.1 cm²

• 19.81 cm²

• 28.26 cm²

If Given Diameter You MUST Divide by 2 FIRST to get the Radius

Find the Area

 $Area\ =\ \pi r^2\ \ or\ \ 3.14\times r\times r$  

This problems gives DIAMETER not radius. Radius is half of diameter.

d= 12
r= 6

 $Area=\ 3.14\times6\times6$  
 $Area=\ 113.04$  

Multiple Choice

What is the radius of this circle?

• 20
• 10
• 40

Multiple Choice

What is the area of this circle?

• 1256

• 31

• 314

• 123

Multiple Choice

What is the radius of this circle?

• 18
• 10
• 9
• 8

Multiple Choice

What is the area of this circle?

• 1017.36

• 254.34

• 56052

• 9

Application: Real World Problems

• Identify Key Words "cover" "area" "take up space"

• Identify the radius (when given diameter YOU MUST DIVIDE BY 2 TO GET THE VALUE OF THE RADIUS before solving)

• Apply to formula:  $Area\ =\ \pi r^2\ \ or\ \ Area\ =\ 3.14\times r\times r$  

Multiple Choice

Shring's dining room table is round and has a radius of 4.5 feet. What is the tabletop's area?

• 63.585 ft²
• 68.345 ft²
• 64.585 ft²
• 61.345 ft²

Multiple Choice

A dog is tied to a wooden stake in a yard. His leash is 3 m long, and he runs around in circles pulling the leash as far as it can go. How much area does the dog have to run around in?

• $$18.84\ m^2$$

• $$84.78\ m^2$$

• $$28.26\ m^2$$

• $$29.01\ m^2$$

Multiple Choice

A lawn sprinkler sprays water 5 ft in every direction as it rotates. What is the area of the sprinkled lawn?

• $$78.5\ ft^2$$

• $$39.25\ ft^2$$

• $$15.7\ ft^2$$

• $$80.1\ ft^2$$

Multiple Choice

Jalen skates at a circular rink that has a radius of 4 yards. If he uses 3.14 for

$$\pi,$$  what area would he estimate for the skating rink?

• 50.24  $$yds^2$$  

• 25.12 $$yds^2$$  

• 38.92  $$yds^2$$  

• 4.13  $$yds^2$$   

Multiple Choice

Mrs. Apple just bought a new dinning room table. She needs to make a table cloth for decoration. What amount of fabric should she buy if the table has a diameter of 5 feet? Choose the equation that would best help solve this problem.

• C = π5

• C = (2)(π)(2.5)

• A = π x 5 x 5

• A = π x 2.5 x 2.5

Multiple Choice

Mrs. Apple just bought a new dinning room table. She needs to make a table cloth for decoration. What amount of fabric should she buy if the table has a diameter of 5 feet?

• C = 15.7

• C = 30.14

• A =78.5

• A = 19.625

Multiple Choice

A clock face has a diameter of 10 inches. What is the approximate area of the clock face in square inches?

• 314 in²

• 31.4 in²

• 7.85 in²

• 78.5 in²

Multiple Choice

A cruise ship has a large, circular window. It has a diameter of 6 meters. What is the window's area?

• 31.25 m²
• 29.55 m²
• 30.36 m²
• 28.26 m²