The ratio of the radii of two circles is 2:3. The diameter of the smaller circle is 15 mm. What is the length of the diameter of the larger circle?

The radii are in the ratio 2:3, so the larger circle’s radius is 3/2 times the smaller circle’s. Diameters have the same ratio as radii, so the larger diameter is 15 × 3/2 = 22.50 mm, choice C.

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