Exams › SSC CGL (Prelims) › General

An annular ring-shaped disc has outer and inner radii of 12 cm and 8 cm. What percentage of the full circle is this ring?

1. 44.44%
2. 55.56%
3. 66.67%
4. 77.78%

Correct answer: 55.56%

Solution

The ring’s area is \(\pi(R^2-r^2)\) and the full outer circle’s area is \(\pi R^2\). So percentage = \(\frac{12^2-8^2}{12^2}\times 100 = \frac{80}{144}\times 100 = 55.56\%\).

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