An aluminum plate is:outer radius 12 inches, inner radius 5 inches. Use 3.14 as an approximate value: How many square inches in the plate? And If the cost to construct the plate is $5.50 per square inch, what is the construction cost?

I think they used the wrong word here. I think it should be called a ring or a washer.

The area of a circular plate is found using A = \pi R^2 . To find the area of a circular plate with a circular hole in it, find the area of a solid plate using the outer radius, then subtract the area of the hole. Then multiply the resulting area by the cost per square inch.

Post back with what you get as an answer, and we'll check it for you.

the area of a circular plate is found using a = \pi r^2 . To find the area of a circular plate with a circular hole in it, find the area of a solid plate using the outer radius, then subtract the area of the hole. Then multiply the resulting area by the cost per square inch.

Post back with what you get as an answer, and we'll check it for you.

lost!

OK, let's start slow. What's the area of a circle of radius 12 inches? I bet you can find an example of this calculation in your text book...

OK, let's start slow. What's the area of a circle of radius 12 inches? I bet you can find an example of this calculation in your text book ...

3.14 12x5
12-5=7

3.14 12x5
12-5=7

seven square inches?
7x5.50=$38.50??

That is not it.

The area of the larger circle is given by the formula ebaines gave you, that is:

A = \pi r^2

So, the larger area is: A = 3.14 \times (12)^2 = 452.16 in^2

Now, find the smaller area.