Cost of polishing all $6$ faces of a cube of edge $4$ cm at Rs. $5$ per cm$^{2}$ is

Cost of polishing all $6$ faces of a cube of edge $4$ cm at Rs. $5$ per cm$^{2}$ is
  1. Rs. $480$
  2. Rs. $320$
  3. Rs. $80$
  4. Rs. $96$

Solution

Surface $= 6 \times 16 = 96$. Cost $= 96 \times 5 = 480$.

Asked in: IMO

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