Circles

The areas of the two circles are in the ratio 2:20. The larger circle has a diameter 20. Calculate the radius of the smaller circle.

Correct answer:

r =  3.2

Step-by-step explanation:

$$\begin{gathered} {\displaystyle \frac{S_1}{S_2}}={\displaystyle \frac{\pi r^2}{\pi {\displaystyle \frac{20}{2}}}}={\displaystyle \frac{2}{20}} \\ r=\sqrt{{\displaystyle \frac{2}{20}}}\cdot {\displaystyle \frac{20}{2}}\doteq 3.2 \end{gathered}$$

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