Instructions

Study the following information to answer these questions.
A cube is coloured red on two opposite faces, blue on two adjacent faces and yellow on the two remaining faces. It is then cut into two halves along the plane parallel to the red faces. One piece is then cut into four equal cubes and the other one into 32 equal cubes

Question 115

How many cubes do not have any coloured face?

Solution

Let's take the original side length of the cube to be 2a

Cutting the square parallel to the red faces, would give us:

image

Let's say we cut the upper piece into four equal squares.

The upper piece is a cuboid with dimensions (2a, 2a, a)
To make four cubes we can cut it into equal halves along is height and length.

image

To cut the lower piece into 32 equal pieces, we can put 3 cuts along its length, 3 cuts along its height and breadth

image

All the cubes from the upper half have at least one face coloured. 
In the lower half, the cubes on the bottom, frontleft, and right would have one face coloured. 
The only cubes that will not have any face coloured would be the four cubes that form the inner portion of the upper face. 

Therefore, 4 is the correct answer. 


cracku

Boost your Prep!

Download App