src_saurav wrote:A cube of white styrofoam is painted red and then cut in half parallel to a pair of parallel sides to form two rectangular solids of equal volume .What percent of the surface area of each of the new solids is not painted red?
1)15%
2)16 2/3
3)20%
4)25%
5)33 1/3%
Surface area of a rectangular solid = 2(lw + lh + wh)
Let each edge of the painted cube have a length of 2, as shown in the following figure:
The blue square represents the cut that splits the cube in half.
In the left half of the cut cube, only the blue square is not painted.
.
Total surface area of the left half of the cut cube = 2(2*1 + 2*2 + 1*2) = 16.
Area of the unpainted blue square = 2*2 = 4.
Thus:
(unpainted area)/(total surface area) = 4/16 = 25%.
The correct answer is
D.
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