Pre-Algebra : Area of a Circle

Study concepts, example questions & explanations for Pre-Algebra

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Example Questions

Example Question #71 : Area Of A Circle

Aliens attacked a farm and left a crop circle. The diameter of the crop circles is  feet, what is the area of this crop circle?

Possible Answers:

Correct answer:

Explanation:

It is important here to understand the equation for the area of a circle which is,

You are given diameter, not radius so you need to half the diameter to get the radius, then plug it in, so:

 = 

Example Question #72 : Area Of A Circle

If a circular island has a diameter of 12 miles, what is the area of the island?

Possible Answers:

Correct answer:

Explanation:

The formula for the area of a circle is  ("" is for radius). However, the question only gives us the diameter, so we must determine the radius ourselves first.

A radius is half a diameter, therefore if the diameter is 12 miles then the radius is 6 miles.

Now we can plug in 6 for "" and solve.

Example Question #11 : How To Find The Area Of A Circle

What is the area of a circle with a diameter of , rounded to the nearest whole number?

Possible Answers:

\dpi{100} 81

\dpi{100} 64

\dpi{100} 255

\dpi{100} 254

Correct answer:

\dpi{100} 64

Explanation:

The formula for the area of a circle is

\dpi{100} \pi r^{2}

Find the radius by dividing 9 by 2:

\dpi{100} \frac{9}{2}=4.5

So the formula for area would now be:

\dpi{100} \pi r^{2}=\pi (4.5)^{2}=20.25\pi \approx 63.6= 64

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