Mensurationhard · Past Paper
The area of an annulus is 100*pi. If outer radius is 15, inner radius is:
A5*sqrt(5)
B5
C10
Dsqrt(125)
✓ Correct Answer: A — 5*sqrt(5)
pi(225 - r^2) = 100*pi => 225 - r^2 = 100 => r^2 = 125 => r = 5*sqrt(5).
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