Surface area of combined cube

CMAT 2019 · Quantitative Techniques & Data Interpretation · Easy · Mensuration

Three solid cubes of sides 1 cm1\text{ cm}, 6 cm6\text{ cm} and 8 cm8\text{ cm} are melted to form a new cube. Find the surface area of the cube so formed.

  1. A.

    729 cm2729\text{ cm}^2

  2. B.

    486 cm2486\text{ cm}^2

  3. C.

    125 cm2125\text{ cm}^2

  4. D.

    529 cm2529\text{ cm}^2

Answer

B

Explanation

Total volume =13+63+83=1+216+512=729 cm3= 1^3 + 6^3 + 8^3 = 1 + 216 + 512 = 729\text{ cm}^3. Side of new cube a=7293=9 cma = \sqrt[3]{729} = 9\text{ cm}.

Surface area =6a2=6×92=6×81=486 cm2= 6a^2 = 6 \times 9^2 = 6 \times 81 = 486\text{ cm}^2.

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