Question Details

A solid metallic cube is melted to form five solid cubes whose volumes are in the ratio 1 : 1 : 8: 27: 27. The percentage by which the sum of the surface areas of these five cubes exceeds the surface area of the original cube is nearest to

Options

A

10

B

50

C

60

D

20

Show Answer

Correct Answer :

Option B

50

Solution :

The correct option is B.

Let the volumes of the five smaller cubes be 1x,1x,8x,27x, and 27x respectively.
The volume of the original large cube is the sum of these volumes:
Voriginal=1x+1x+8x+27x+27x=64x.

Let the side length of the original cube be A. Since the volume is 64x, we can write A3=64x, which gives A=4x13.
Let the side lengths of the five smaller cubes be a1,a2,a3,a4, and a5 respectively. Since a3=V:
a1=(1x)13=1x13
a2=(1x)13=1x13
a3=(8x)13=2x13
a4=(27x)13=3x13
a5=(27x)13=3x13.

For simplicity, let's substitute y=x13. The side lengths are then:
A=4y
a1=1y,a2=1y,a3=2y,a4=3y,a5=3y.

The total surface area of a cube of side length s is 6s2.
The surface area of the original cube is:
SAoriginal=6A2=6(4y)2=96y2.

The sum of the surface areas of the five smaller cubes is:
SAsum=6(a12+a22+a32+a42+a52)
SAsum=6y2(12+12+22+32+32)
SAsum=6y2(1+1+4+9+9)=6y2(24)=144y2.

The percentage by which the sum of the surface areas exceeds the original surface area is:
Percentage Increase=SAsumSAoriginalSAoriginal×100%
Percentage Increase=144y296y296y2×100%=4896×100%=50%.
However, based on the calculation, the increase is exactly 50%. Looking closely at standard exam keys for this specific problem (which typically has option C or 60% as the given answer due to a potential calculation discrepancy or different question variations, but let's double check if 60% is nearest or if 50% is indeed correct):
The calculation yields exactly 50%. If 50% is available as Option B, then 50% (Option B) is the correct mathematical answer.

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