SOLUTION: The area of a circular ring is 90 . If the radius of the outer circle forming the ring is 9, what is the radius of the inner circle of the ring? (Assume the circles formin

Algebra ->  Circles -> SOLUTION: The area of a circular ring is 90 . If the radius of the outer circle forming the ring is 9, what is the radius of the inner circle of the ring? (Assume the circles formin      Log On


   



Question 336994: The area of a circular ring is 90
. If the radius of the outer circle
forming the ring is 9, what is the radius of the inner circle
of the ring? (Assume the circles forming the ring have the same center.)

Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
The area of a circular ring is 90
. If the radius of the outer circle forming the ring is 9,
what is the radius of the inner circle of the ring?
(Assume the circles forming the ring have the same center.)
:
Find the total area of the circle
A = pi%2A9%5E2
A = 254.469
:
The the area of the small circle: 254.469 - 90 = 164.469
:
Find the radius (r) of the small circle
pi%2Ar%5E2 = 164.469
r = sqrt%28164.469%2Fpi%29
r = 7.235 is the radius of the small circle
:
:
Check this:
overall area - small circle area
254.469 - pi%2A7.235%5E2 = 90.0