The diameter of a planet is about 25,464 mi. The diameter of the planet's moon is about 21 % of the diameter of the planet. What percent of the volume of the planet is the volume of its moon?

The diameter of the moon:

25,464 (.21) = 5,347.44

The radius of the moon:

5,347.44/2 = 2,673.72

The volume of the moon:

80,063,834,021.277

The volume of the planet:

8,645,268,763,770.284

80,063,834,021.277 / 8645268763770.284 = 0.009261

0.0092%