A large cube is formed from the material obtained by melting three smaller cubes of 3, 4 and 5 cm side. What is the ratio of the total surface areas of the smaller cubes and the large cube?

A. 2 : 1 B. 3 : 2
C. 25 : 18 D. 27 : 20

• Ans: Option C=25:18
  The total volume of the smaller cubes=216 cm^3(3^3+4^3+5^3)
  Now, the side of the bigger cube is 6cm
  The total surface area of the smallers cubes= 300 cm^2(6*3^2+6*4^2+6*5^3)
  The total surface area of the bigger cube= 216 cm^2(6*6^2)
  Now the ratio as asked is 300cm^2:216 cm^2=25:18
• 12 years agoHelpfull: Yes(2) No(5)
• Volume of the large cube = (33 + 43 + 53) = 216 cm3.
  
  Let the edge of the large cube be a.
  
  So, a3 = 216 a = 6 cm.
  
  Required ratio = 6 x (3^2 + 4^2 + 5^2) / 6*(6^2) = 25 : 18.
  
• 9 years agoHelpfull: Yes(2) No(1)