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1. The ratio of the radii of two circles is 1 : 3. Then the ratio of their areas is :

A. 1 : 3

B. 1 : 6

C. 1 : 9

D. None of these

Solution:

Let the radii of the two circle be r and 3r respectively.
Then, required ratio :

= \frac{π r^{2}}{π {(3 r)}^{2}} = \frac{π r^{2}}{9 π r^{2}} = 1 : 9

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