Question 32
Mensuration of Plane ShapesIn the diagram above are two concentric circles of radii r and R respectively with centre O. If r = (2/5)R, express the area of the shaded portion in terms of π and R.
- A.(21/25)πR2
- B.(9/25)πR2
- C.(21/23)πR2
- D.(5/9)πR2
Show the answer and explanation
Answer: A ((21/25)πR2)
Explanation
The shaded ring has area πR2 − πr2 = πR2 − (4/25)πR2 = (21/25)πR2.