Area of Shaded Region Concentric Circles

How to find the area of a shaded region if the circles are concentric.

[cyeisha]

Thank you so much, I have a big test today (nwea) and I did NOT know how to do it. This is gonna help me out alot.

[nukya]

Thanks! I'm helping my son study for a test and this really clear things up.

[willsweeney]

This helped, didn't realize it was this easy!

[sebastianrietveld]

30x30 is 900 but you didn’t multiply the pie with that can someone help me

[iantuurttelll]

Thank you this is one of the last things I need to know for finals

[heywillubemyfriend]

Thanks for this, it really helped me because I'm really BAD at

[pol_dat_boi]

Nice explanation! I appreciate the help.

[winter]

Thank you a lot...this has helped me so much for my test today. Thanks again😀😊

[moosie]

Thanks so much I have been stuck in a question like this for hours

[briansolloway]

Try this simple method, in only 3 calculations to get the answer. We used this in my office 65 years ago when we were calculating the area of a cross section of a tube. So imagine that your drawing is a tube. FORMULA = o/d minus gauge X Pi X gauge.
o/d is the outside diameter of the tube. The gauge is what we called the thickness of the wall of the tube.
So in your example the o/d would be 120 cm and the thickness would be 30 cm.
So 120 minus 30 x Pi (3.14) x 30 = Answer 8478 sq. cm.
So let me know what you think.

[maryserwaa]

It really helped a lot I was able to complete my work easily and faster than usual.

[serenelai]

Thanks for letting me learn this complicated skill when I'm Grade 4

[heywillubemyfriend]

One more thing, what if the two radiuses are disconnected???

[JackassJunior]

Question and this is a problem with your method. What abut with decimals? I have a question to work our the shaded area, the larger circle has a radius of 4.1 whereas the smaller one has a radius of 1.7. Now this is where I am having a problem with your method, the answer has to be given to 3 significant figures. Now I can work out the areas of both circles thanks to Pi, however the resulting answer as a whole does not give me the availability to give the answer to 3 significant figures.

[ibunkunoluwaosideko]

Are we meant to mutiply the answer by 3.14 or leave the answer in 2700^?

[PigglyWiggly]

Thank you that really clarified it for me :)

[gloriakalengelayi]

I don’t understand how you got the answer I thought to work out an area of a circle is radius^ times pie (3.14) and to get the area of the shaded area You minus the area for the smaller circle 60^=3600x3.14=11, 304 - 30^=900x3.14=2826 So it’s 11, 304 - 2826= 8478 so how did you get the other answer

[banana]

What if only the radius of the small circle is given? How do you find the radius of the big circle?

[cheesekuh]

...so what's the area of the circle is the bigger portion measures r= 30 inches and the smaller part measures r= 40 inches?

[dinahmite]

I'm studying right now and doing a question where the radius of the circles arent given. Only the tangent of the smaller circle where it hits the bigger circle. The distance between those 2 points are given. I have no idea how to do it. Any idea?!?!?