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A cube of side 10 cm is coloured red with a 2 cm wide green strip along all the sides on all the faces. The cube is divided into 125 smaller cubes of equal size. Answer the following questions based on this statement.How many cubes have at least one face coloured?

Question

A cube of side 10 cm is coloured red with a 2 cm wide green strip along all the sides on all the faces. The cube is divided into 125 smaller cubes of equal size. Answer the following questions based on this statement.How many cubes have at least one face coloured?

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Solution 1

The cube is divided into 125 smaller cubes, which means it is divided into 5 cubes along each edge (since 555 = 125).

  1. The cubes on the corners will have three faces coloured. There are 8 corners on a cube, so 8 cubes will have three faces coloured.

  2. The cubes along the edges (excluding the corners) will have two faces coloured. Each edge of the cube has 5 cubes, but we exclude the corners, so each edge has 3 cubes with two faces coloured. A cube has 12 edges, so there are 12*3 = 36 cubes with two faces coloured.

  3. The cubes on the faces (excluding the edges) will have one face coloured. Each face of the cube has 55 = 25 cubes, but we exclude the edges, so each face has 33 = 9 cubes with one face coloured. A cube has 6 faces, so there are 6*9 = 54 cubes with one face coloured.

So, the total number of cubes with at least one face coloured is 8 (corners) + 36 (edges) + 54 (faces) = 98 cubes.

This problem has been solved

Solution 2

The cube of side 10 cm is divided into 125 smaller cubes. This means each smaller cube has a side of 2 cm (since 10 cm / 5 = 2 cm).

The green strip is 2 cm wide, which means it covers one whole smaller cube on each side of the larger cube.

  1. The smaller cubes on the corners will have three faces coloured. There are 8 corners on a cube, so 8 smaller cubes have three faces coloured.

  2. The smaller cubes along the edges (excluding the corners) will have two faces coloured. Each edge of the cube has 3 such smaller cubes (since 5 cubes total - 2 corners = 3). Since a cube has 12 edges, there are 12 * 3 = 36 smaller cubes with two faces coloured.

  3. The smaller cubes on the faces (excluding the edges and corners) will have one face coloured. Each face of the cube has 9 such smaller cubes (since 25 cubes total - 16 cubes on edges and corners = 9). Since a cube has 6 faces, there are 6 * 9 = 54 smaller cubes with one face coloured.

So, the total number of smaller cubes that have at least one face coloured is 8 (corners) + 36 (edges) + 54 (faces) = 98.

This problem has been solved

Solution 3

The cube is divided into 125 smaller cubes, which means it is divided into 5 cubes along each edge (since 555 = 125).

  1. The cubes on the corners will have three faces coloured. There are 8 corners on a cube, so 8 cubes have three faces coloured.

  2. The cubes along the edges, not including the corners, will have two faces coloured. Each edge of the cube has 5 cubes, but we've already counted the 2 at the corners, so there are 3 cubes along each edge that have two faces coloured. A cube has 12 edges, so there are 3*12 = 36 cubes with two faces coloured.

  3. The cubes on the faces of the cube, not including the edges, will have one face coloured. Each face of the cube has 55 = 25 cubes, but we've already counted the 16 cubes along the edges and corners, so there are 25 - 16 = 9 cubes on each face that have one face coloured. A cube has 6 faces, so there are 96 = 54 cubes with one face coloured.

So, in total, there are 8 + 36 + 54 = 98 cubes that have at least one face coloured.

This problem has been solved

Solution 4

The cube of side 10 cm is divided into 125 smaller cubes, which means each smaller cube has a side of 2 cm (since 10 cm / 2 cm = 5 cubes per side).

The green strip is 2 cm wide, which means it covers one whole smaller cube on each side of the larger cube.

  1. The cubes on the corners will have three faces coloured. There are 8 corners on a cube, so 8 smaller cubes have three faces coloured.

  2. The cubes along the edges (excluding the corners) will have two faces coloured. Each edge of the cube has 3 such smaller cubes (5 cubes per edge - 2 corner cubes = 3 cubes). Since a cube has 12 edges, there are 12 * 3 = 36 smaller cubes with two faces coloured.

  3. The cubes on the faces (excluding the edges) will have one face coloured. Each face of the cube has 9 such smaller cubes (5 cubes per side - 22 edge cubes = 1 cube, and 11 = 1 square of cubes). Since a cube has 6 faces, there are 6 * 9 = 54 smaller cubes with one face coloured.

So, the total number of smaller cubes that have at least one face coloured is 8 (corners) + 36 (edges) + 54 (faces) = 98 cubes.

This problem has been solved

Solution 5

The cube of side 10 cm is divided into 125 smaller cubes of equal size. This means that each smaller cube has a side of 2 cm (since 10 cm / 5 = 2 cm).

The green strip is 2 cm wide, which means it covers one layer of smaller cubes on each face of the larger cube.

  1. The cubes on the corners will have three faces coloured. There are 8 corners on a cube, so 8 smaller cubes have three faces coloured.

  2. The cubes along the edges (excluding the corners) will have two faces coloured. Each edge of a cube has 3 smaller cubes (since 10 cm / 2 cm = 5 cubes, but we exclude the corners), and a cube has 12 edges, so 12 * 3 = 36 smaller cubes have two faces coloured.

  3. The cubes on the faces (excluding the edges) will have one face coloured. Each face of a cube has 9 smaller cubes (since 3*3 = 9), and a cube has 6 faces, so 6 * 9 = 54 smaller cubes have one face coloured.

So, the total number of smaller cubes that have at least one face coloured is 8 (corners) + 36 (edges) + 54 (faces) = 98.

This problem has been solved

Solution 6

The cube is divided into 125 smaller cubes, which means it is divided into 5 cubes along each edge (since 555 = 125).

  1. The cubes on the corners will have three faces coloured. There are 8 corners on a cube, so 8 cubes will have three faces coloured.

  2. The cubes along the edges (excluding the corners) will have two faces coloured. Each edge of the cube has 5 cubes, but we exclude the corners, so there are 3 cubes per edge that have two faces coloured. There are 12 edges on a cube, so 12*3 = 36 cubes will have two faces coloured.

  3. The cubes on the faces (excluding the edges and corners) will have one face coloured. Each face of the cube has 55 = 25 cubes, but we exclude the edges and corners, so there are 25 - 9 = 16 cubes per face that have one face coloured. There are 6 faces on a cube, so 616 = 96 cubes will have one face coloured.

So, in total, there are 8 + 36 + 96 = 140 cubes that have at least one face coloured.

This problem has been solved

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