GED Math : Area of a Circle

Study concepts, example questions & explanations for GED Math

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Example Questions

Example Question #131 : 2 Dimensional Geometry

Find the area of a circle with a diameter of 18.

Possible Answers:

\displaystyle 81\pi

\displaystyle 162\pi

\displaystyle 18\pi

\displaystyle 324\pi

\displaystyle 108\pi

Correct answer:

\displaystyle 81\pi

Explanation:

Write the formula for the area of a circle.

\displaystyle A = \pi r^2

The radius is half the diameter, or \displaystyle \frac{18}{2} = 9.

Substitute the radius.

\displaystyle A = \pi (9)^2 = 81\pi

The answer is:  \displaystyle 81\pi

Example Question #41 : Area Of A Circle

Find the area of a circle with a radius of \displaystyle 2x+1.

Possible Answers:

\displaystyle 4x^2+4x +1

\displaystyle 4\pi x^2+4\pi x +\pi

\displaystyle 4\pi x^2+1

\displaystyle 4\pi x^2+\pi

\displaystyle 4\pi x^2+4\pi x +1

Correct answer:

\displaystyle 4\pi x^2+4\pi x +\pi

Explanation:

Write the formula for the area of a circle.

\displaystyle A =\pi r^2

Substitute the radius.

\displaystyle A =\pi (2x+1)^2 = (2x+1) (2x+1) \pi

Use the FOIL method to simplify the binomials.

\displaystyle (2x+1) (2x+1) = (2x)(2x) + (2x)(1) + (1)(2x)+(1)(1)

Simplify the terms.

\displaystyle 4x^2+2x+2x+1 = 4x^2+4x +1

Multiply this quantity by pi.

\displaystyle \pi (4x^2+4x +1)

The answer is:  \displaystyle 4\pi x^2+4\pi x +\pi

Example Question #41 : Area Of A Circle

Find the area of a circle with a radius of \displaystyle 3\pi ^8.

Possible Answers:

\displaystyle 9\pi^{16}

\displaystyle 9\pi^{65}

\displaystyle 9\pi^{64}

\displaystyle 9\pi^{17}

Correct answer:

\displaystyle 9\pi^{17}

Explanation:

Write the formula for the area of a circle.

\displaystyle A= \pi r^2

Substitute the radius into the equation.

\displaystyle A= \pi (3\pi ^8)^2= \pi (3\pi ^8)(3\pi ^8)

The answer is:  \displaystyle 9\pi^{17}

Example Question #132 : Geometry And Graphs

Find the area of a circle with a radius of 25.

Possible Answers:

\displaystyle 50\pi

\displaystyle 150\pi

\displaystyle 125\pi

\displaystyle 525\pi

\displaystyle 625 \pi

Correct answer:

\displaystyle 625 \pi

Explanation:

Write the formula for the area of a circle.

\displaystyle A=\pi r^2

Substitute the radius.

\displaystyle A=\pi (25)^2 = \pi (25)(25) = 625 \pi

The answer is:  \displaystyle 625 \pi

Example Question #141 : 2 Dimensional Geometry

Determine the area of a circle with a radius of \displaystyle 20.

Possible Answers:

\displaystyle 400 \pi

\displaystyle 40\pi

\displaystyle 40\pi

\displaystyle 1600\pi

\displaystyle 140\pi

Correct answer:

\displaystyle 400 \pi

Explanation:

Write the formula for the area of a circle.

\displaystyle A =\pi r^2

Substitute the radius.

\displaystyle A =\pi (20)^2

The answer is:  \displaystyle 400 \pi

Example Question #1102 : Ged Math

Find the area of a circle with a radius of 7in.

Possible Answers:

\displaystyle 28\pi \text{ in}^2

\displaystyle 14\pi \text{ in}^2

\displaystyle 21\pi \text{ in}^2

\displaystyle 3.5\pi \text{ in}^2

\displaystyle 49\pi \text{ in}^2

Correct answer:

\displaystyle 49\pi \text{ in}^2

Explanation:

To find the area of a circle, we will use the following formula:

\displaystyle A = \pi r^2

where r is the radius of the circle.

Now, we know the radius of the circle is 7in. So, we can substitute. We get

\displaystyle A = \pi \cdot (7\text{in})^2

\displaystyle A = \pi \cdot 49\text{in}^2

\displaystyle A = 49\pi \text{ in}^2

Example Question #47 : Area Of A Circle

Let \displaystyle \pi = 3.14

Find the area of a circle with a diameter of 8in.

Possible Answers:

\displaystyle 100.48\text{in}^2

\displaystyle 25.12\text{in}^2

\displaystyle 200.96\text{in}^2

\displaystyle 50.24\text{in}^2

\displaystyle 153.86\text{in}^2

Correct answer:

\displaystyle 50.24\text{in}^2

Explanation:

To find the area of a circle, we will use the following formula:

\displaystyle A = \pi \cdot r^2

where r is the radius of the circle.

Now, we know \displaystyle \pi = 3.14. We know the diameter of the circle is 8in. We know the diameter is two times the radius. Therefore, the radius is 4in. So, we substitute. We get

\displaystyle A = 3.14 \cdot(4\text{in})^2

\displaystyle A = 3.14 \cdot 16\text{in}^2

\displaystyle A = 50.24\text{in}^2

Example Question #141 : 2 Dimensional Geometry

Determine the area of a circle with a radius of \displaystyle 9\sqrt{2}.

Possible Answers:

\displaystyle 162\pi

\displaystyle 162

\displaystyle 81

\displaystyle 81\pi

Correct answer:

\displaystyle 162\pi

Explanation:

Write the formula for the area of a circle.

\displaystyle A=\pi r^2

Substitute the radius.

\displaystyle A=\pi (9\sqrt{2})^2=\pi (9\sqrt{2})(9\sqrt{2}) = 81\cdot 2 \pi

The answer is:  \displaystyle 162\pi

Example Question #44 : Area Of A Circle

Find the area of a circle with a diameter of \displaystyle \sqrt{5}.

Possible Answers:

\displaystyle \pi\sqrt{10}

\displaystyle \frac{5}{2}\pi

\displaystyle \frac{5}{8}\pi

\displaystyle \pi\sqrt5

\displaystyle \frac{5}{4}\pi

Correct answer:

\displaystyle \frac{5}{4}\pi

Explanation:

Write the formula for the area of the circle.

\displaystyle A=\pi r^2

The radius is half the diameter.

\displaystyle r= \frac{d}{2} = \frac{\sqrt5}{2}

Substitute the radius.

\displaystyle A=\pi (\frac{\sqrt5}{2})^2 = \pi (\frac{\sqrt5}{2})(\frac{\sqrt5}{2})

The answer is:  \displaystyle \frac{5}{4}\pi

Example Question #41 : Area Of A Circle

Find the area of a circle with a diameter of 16.

Possible Answers:

\displaystyle 16\pi

\displaystyle 64\pi

\displaystyle 32\pi

\displaystyle 96\pi

\displaystyle 128\pi

Correct answer:

\displaystyle 64\pi

Explanation:

Write the formula for the area of a circle.

\displaystyle A = \pi r^2

The radius of the circle is half the diameter, or 8.

Substitute the radius into the equation.

\displaystyle A = \pi (8)^2 = 64\pi

The answer is:  \displaystyle 64\pi

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