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Consider a cuboid of sides 2x, 4x and 5x and a closed hemisphere of radius r. If the sum of their surface areas is a constant k, then the ratio x : r, for which the sum of their volumes is maximum, is

1. 2 : 5
2. 19 : 45
3. 3 : 8
4. 19 : 15

Correct answer: 19 : 45

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