2012 · Q82
The area enclosed between the circumferences of two concentric circles is 16*pi cm^2 and their radii are in the ratio 5:3. What is the area of the outer circle?
Elementary MathematicsMensuration
- A9*pi cm^2
- B16*pi cm^2
- C25*pi cm^2
- D36*pi cm^2
Explanation
pi(25k^2-9k^2) = 16*pi gives k = 1; outer radius 5, area 25*pi.