Question 1105282
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All spheres are similar.  For any similar figures, if the ratio of linear measurements (scale factor) is a:b, then the ratio of area measurements is a^2:b^2 and the ratio of volume measurements is a^3:b^3.<br>
The radius of a sphere is a linear measurement; if the ratio of the radii of two spheres is 5:3, then the ratio of the volumes is 5^3:3^3 = 125:27.