An annular region has outer radius 12 cm and inner radius 8 cm. What is the approximate ratio of the annular area to the whole outer circle?

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Accepted Answer

1. Area of annulus = $\pi(R^2-r^2)$. 
2. Here $R=12$, $r=8$, so $R^2-r^2=144-64=80$. Annulus = $80\pi$. 
3. Outer circle area = $144\pi$. 
4. Ratio = $80\pi:144\pi = 80:144 = 5:9$. 
FINAL_ANSWER: b

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