Areas of Circles 1
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Question 1 of 5
1. Question
Find the area of the circle
Round your answer to `1` decimal placeUse `pi=3.14`- `\text(Area )=` (78.5, 78.6) `cm^2`
Hint
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Well Done!
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Area of a Circle Formula
`\text(Area)=pi times``\text(radius)^2`Given Lengths
`\text(radius)=5`
Solve for the area using the formula: `A=pi``r^2`Use `pi=3.14` See `pi` explained`\text(Area)` `=` `pi times``\text(radius)^2` Area of a Circle Formula `=` `3.14 times ``5^2` Plug in the known values `=` `3.14 times 25` Evaluate `=` `78.5 cm^2` The given measurements are in centimetres, so the area is measured as square centimetres`\text(Area)=78.5 cm^2`The answer will depend on which `pi` you use.In this solution we used: `pi=3.14`.Using Answer `pi=3.14` `78.5 cm^2` `pi=3.141592654` `78.5 cm^2` `pi=(22)/(7)` `78.6 cm^2` -
Question 2 of 5
2. Question
Find the area of the circle
Round your answer to `1` decimal placeUse `pi=3.14`- `\text(Area )=` (346.2, 346.4, 346.5) `m^2`
Correct
Great Work!
Incorrect
Area of a Circle Formula
`\text(Area)=pi times``\text(radius)^2`Given Lengths
`\text(diameter)=21`
First, find the radius of the circle. Note that the radius is half of the diameter`\text(radius)` `=` $$\frac{\color{#00880a}{\text{diameter}}}{2}$$ `=` $$\frac{\color{#00880a}{\text{21}}}{2}$$ `\text(radius)` `=` `10.5` Finally, solve for the area using the formula: `A=pi``r^2`Use `pi=3.14` See `pi` explained`\text(Area)` `=` `pi times``\text(radius)^2` Area of a Circle Formula `=` `3.14 times ``10.5^2` Plug in the known values `=` `3.14 times 110.25` Evaluate `=` `346.185` `=` `346.2 m^2` Rounded to `1` decimal place The given measurements are in metres, so the area is measured as square metres`\text(Area)=346.2 m^2`The answer will depend on which `pi` you use.In this solution we used: `pi=3.14`.Using Answer `pi=3.14` `346.2 m^2` `pi=3.141592654` `346.4 m^2` `pi=(22)/(7)` `346.5 m^2` -
Question 3 of 5
3. Question
Find the area of the Circle
Round your answer to `1` decimal placeUse `pi=3.14`- `\text(Area )=` (149.5, 149.6) `km^2`
Correct
Keep Going!
Incorrect
Area of a Circle Formula
`\text(Area)=pi times``\text(radius)^2`Given Lengths
`\text(diameter)=13.8`
First, find the radius of the circle
Note that the radius is half of the diameter`\text(radius)` `=` $$\frac{\color{#00880a}{\text{diameter}}}{2}$$ `=` $$\frac{\color{#00880a}{\text{13.8}}}{2}$$ `\text(radius)` `=` `6.9` Finally, solve for the area using the formula: `A=pi``r^2`Use `pi=3.14` See `pi` explained`\text(Area)` `=` `pi times``\text(radius)^2` Area of a Circle Formula `=` `3.14 times ``6.9^2` Plug in the known values `=` `3.14 times 47.61` Evaluate `=` `149.4954` `=` `149.5 km^2` Rounded to `1` decimal place The given measurements are in kilometres, so the area is measured as square kilometres`\text(Area)=149.5 km^2`The answer will depend on which `pi` you use.In this solution we used: `pi=3.14`.Using Answer `pi=3.14` `149.5 km^2` `pi=3.141592654` `149.6 km^2` `pi=(22)/(7)` `149.6 km^2` -
Question 4 of 5
4. Question
Find the area of the orange-shaded region.
The given measurements are in centimetres.Round your answer to `1` decimal place.`pi=3.14`- `\text(Area )=` (103.7, 103.6) `cm^2`
Hint
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Area of a Circle Formula
`\text(Area)=pi xx``\text(radius)^2`Given Lengths
`\text(radius)` (Whole Circle)`=7``\text(thickness)` (Shaded Region)`=3`
First, solve for the area of the Whole CircleUse `pi=3.14` See `pi` explained`\text(Area)``\text(Whole Circle)` `=` `pi xx``\text(radius)^2` `=` `3.14 xx``7^2` `\text(Area)` `=` `153.86 cm^2` 
Find the radius of the Inner Circle by subtracting the thickness of the shaded region from the radius of the Whole Circle.`\text(radius)``\text(Inner Circle)` `=` `\text(radius)``-``\text(thickness)` `=` `7``-``3` `=` `4 cm` 
Next, find the area of the Inner Circle`\text(Area)``\text(Inner Circle)` `=` `pi xx``\text(radius)^2` `=` `3.14 times ``4^2` `\text(Area)` `=` `50.24 cm^2` 
Finally, subtract the area of the Inner Circle from the area of the Whole Circle`\text(Final Area)` `=` `153.86``-``50.24` `=` `103.62` `=` `103.6 cm^2` Rounded to `1` decimal place The given measurements are in centimetres, so the area is measured as square centimetres`\text(Area)=103.6 cm^2`The answer will depend on which `pi` you use.In this solution we used: `pi=3.14`.Using Answer `pi=3.14` `103.6 cm^2` `pi=3.141592654` `103.7 cm^2` `pi=(22)/(7)` `103.7 cm^2` -
Question 5 of 5
5. Question
Find the area of the yellow-shaded region.
Round your answer to `1` decimal placeUse `pi=3.14`- `\text(Area )=` (50.2, 50.3) `cm^2`
Hint
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Fantastic!
Incorrect
Area of a Semicircle Formula
`\text(Area)=1/2 xx pi xx``\text(radius)^2`Given Lengths
`\text(radius)` (Whole Semicircle)`=9``\text(thickness)` (Shaded Region)`=2`
First, solve for the area of the Whole SemicircleUse `pi=3.14` See `pi` explained`\text(Area)``\text(Whole Semicircle)` `=` `1/2 xx pi xx``\text(radius)^2` `=` `1/2 xx 3.14 xx``9^2` `\text(Area)` `=` `127.17 cm^2` 
Find the radius of the Inner Semicircle by subtracting the thickness of the shaded region from the radius of the Whole Semicircle.`\text(radius)``\text(Inner Semicircle)` `=` `\text(radius)``-``\text(thickness)` `=` `9``-``2` `=` `7 cm` 
Next, find the area of the Inner Semicircle`\text(Area)``\text(Inner Semicircle)` `=` `1/2 xx pi xx``\text(radius)^2` `=` `1/2 xx 3.14 times ``7^2` `\text(Area)` `=` `76.93 cm^2` 
Finally, subtract the area of the Inner Semicircle from the area of the Whole Semicircle`\text(Final Area)` `=` `127.17``-``76.93` `=` `50.24` `=` `50.2 cm^2` Rounded to `1` decimal place The given measurements are in centimetres, so the area is measured as square centimetres`\text(Area)=50.2 cm^2`The answer will depend on which `pi` you use.In this solution we used: `pi=3.14`.Using Answer `pi=3.14` `50.2 cm^2` `pi=3.141592654` `50.3 cm^2` `pi=(22)/(7)` `50.3 cm^2`