Discussion

Paper charge is Rs. 60 per kg. How much expenditure would be there to cover a cube of edge 10m with a paper, if one kg of paper covers 20 sq.m. area?

Answer: D

Find the area to be covered, convert it to a weight of paper, then price it.

\[ \text{surface area of cube} = 6a^{2} = 6 \times 10^{2} = 600 \text{ m}^{2} \]

\[ \text{paper needed} = \frac{600}{20} = 30 \text{ kg} \]

\[ \text{cost} = 30 \times 60 = \text{Rs. } 1800 \]

All six faces are covered, so the factor is 6 and not 4 - using only the four side faces gives Rs. 1200.

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