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The ratio of the weights of a body on the Earth’s surface to that on the surface of a planets is 9 : 4. The mass of the planet is 9 1 th of that of the Earth. If 'R' is the radius of the Earth, what is the radius of the planet ? (Take the planets to have the same mass density)

1. 9 R
2. 2 R
3. 3 R
4. 4 R

Correct answer: 2 R

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