Question

How do I work this out?

Answer 1

First, find the area of the circle as a whole. Then find the percentage or fraction of that area.

STEP ONE

As you probably know, you use this formula to find the area of any circle.


`A=\pir^2`

We know what the radius is, so substitute the 4 for the r in the formula.


`A=4^2\pi`

Simplify.


`A=4^2\pi`

`A=16\pi`

STEP TWO

Now that we know what the area of the circle is as a whole, let's find the fraction of that area. We want to the know the area of the shaded part.

Multiply the area by 3/4.


`(16\pi)(3/4)`

`(48\pi)/4`

`12\pi`

So, the answer is the first option.

Answer 2

area of a full circle is: PI x r^2

so full circle is 4^2 x PI = 16PI

the shaded part is 3/4 of the circle

16 x 3/4 = 12
so 12 PI ft^2 is shaded