Hi

morya003This problem could be solved easily if we pick some smart numbers (as no numbers are given in the question).

Let's say that the original cube of white chalk had a side of length 2 cm.

The area of a side of the cube will then be 2 x 2 = 4 sq. cm.

The total surface area of the cube will be given by 6 x area of 1 side

i.e. 6 x 4 = 24 sq. cm.

Now, the total surface area represents the area of the cube that has been painted red.

The cube is now cut into half. This means that one of the sides of the newly formed rectangular solid is not painted at all. This area will be equal to the area of the side of the original cube i.e.

4 sq. cm. --->

(1)Since the newly formed rectangular solid is half of the cube, the area that is painted red is given be (area of 1 side of the cube + half of sum of areas of four other sides of the cube)

i.e. 4 + 1/2 * (4 + 4 + 4 + 4) = 4 + 1/2 (16) = 4 + 8 = 12 sq. cm.

The total surface area of the newly formed rectangular solid will be given by the sum of areas of the sides painted red + the area of the side which is not painted

i.e. 4 + 12 =

16 sq. cm --->

(2)Now, we are asked to find the percent of the surface area of each of the new solids which is not painted red.

This will be given by the ratio of the area of the surface not painted red to the total surface area of the new solid i.e. from (1) and (2)

i.e. 4 / 16 =

25%Hence the correct answer is

option DHope this helps

Cheers!

Sudish

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MBA Candidate 2015 | Georgetown University

McDonough School of Business