The area of a circular ring is 90. If the radius is 10, what is the radius of the inner circle of the ring. (Assume the circles forming the ring have the same center.)

- anonymous

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- anonymous

|dw:1326924368144:dw|

- anonymous

A=Pi * r^2

- anonymous

the picture wasnt given by the way...
i drew it myself

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## More answers

- phi

|dw:1326924766289:dw|

- phi

the ring (dashed lines) has area 90. The big circle has area pi*10*10= 100 pi
Subtract the ring from the big circle to get the area of the smaller circle.
now you know A_small_circle= pi * r^2
so
100 pi - 90 = pi r^2
can you solve for r?

- anonymous

continue please

- Hero

Yes, this is not as hard as you think.

- anonymous

yeah, i know. i dont seem to be getting the right answer though.

- Hero

First of all, are you sure you wrote everything down correctly? You were not exactly clear in your original post. You need to state which area of which circle the 90 applies to. You also need to state which radius the 10 applies to.

- anonymous

ok i made one mistake

- anonymous

let me retype the question

- anonymous

The area of a circular ring is 90. If the radius of the outer circle forming the ring is 10, what is the radius of the inner circle of the ring? (Assume the circles forming the ring have the same center.)

- Hero

Which circular ring is 90? The big one or little one?

- anonymous

the prob doesnt say but i am assuming its the while circle (little one included)

- anonymous

|dw:1326927820335:dw|

- anonymous

all of that is 90

- anonymous

i think

- anonymous

*whole circle

- Hero

Why would they give you the area of the big one and then give you the radius of the big one. One of those are in conflict, and I'll prove it to you

- Hero

A = pir^2
90 = pir^2
90/pi = r^2
sqrt(90/pi) = r
see if you get r = 10 from that. I doubt it

- anonymous

i know

- anonymous

thats why im confusded.

- anonymous

*confused

- anonymous

but thats the problem.

- Hero

Well, if it's that bad, don't do the problem.

- Hero

It's clearly ambiguous

- Hero

Is this problem on your computer or in your book?

- anonymous

hw site

- anonymous

https://www.mathclass.org/mc/hw.aspx?WhsAcctId=a10614d4-5e55-4afb-a76f-ee3001ef3e66&classId=2161&hwId=6221&rndSeed=32456754&mode=0&noSVG=0

- anonymous

try this link

- Hero

Nope didn't work. Why do you go to the site and copy screen and save as picture file, then upload here.

- anonymous

how do i do that?

- Hero

I just told you. There should be a "print screen" function on your keyboard. Go to the site and press that. Alternatively find a copy screen program online

- anonymous

hold on. im gonna use excel 2010.

- Hero

Excel? What's that gonna do?

- anonymous

##### 1 Attachment

- anonymous

does it work?

- anonymous

excel has a screenshot option

- Hero

Okay, I understand now.

- Hero

Hold on a sec.

- Hero

r = 8.45
The problem it didn't say whether to use 3.14 for pi or not. By the way, you imagined the area incorrectly initally.

- anonymous

show me how u got that please

- Hero

vyew?

- anonymous

huh?

- Hero

Funny, everyone knows what twiddla is, but no one knows what vyew is

- anonymous

idk either lol

- Hero

http://vyew.com/room#/418625/Open_Study

- Hero

Mario, where are you?

- anonymous

Hero I need help putting in a prob into my hw site... its the latest one i posted

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