Math Problem Statement

A cube is cut in two equal parts along a plane parallel to one of its faces. One piece is then coloured red on the two larger faces and green on the remaining, while the other is coloured green on two smaller adjacent faces and red on the remaining. Each is then cut into 32 cubes of same size and mixed up. 15. How many cubes have two red and one green face on each

Solution

To solve this, let's analyze the problem step-by-step.

Step 1: Understanding the Initial Cube and Cuts

  1. We start with a cube, which is divided into two equal parts along a plane parallel to one of its faces.
  2. Each half of the cube will therefore have two larger faces (the cut faces) and four smaller faces.

Step 2: Coloring the Halves

  1. First half: Colored red on its two larger (cut) faces and green on the remaining four smaller faces.
  2. Second half: Colored green on two adjacent smaller faces and red on the remaining four faces (including the two cut faces).

Step 3: Dividing Each Half into Smaller Cubes

Each half is cut into 32 smaller cubes, so we have a total of 32+32=6432 + 32 = 64 smaller cubes.

Step 4: Finding Cubes with Two Red and One Green Face

  1. To have two red and one green face, a cube must:

    • Be located at the edge between two red faces and one green face.
  2. Let's analyze each half separately:

    • First half: The two large red faces are opposite each other, and the green faces are on the four sides. This arrangement gives exactly 8 edge cubes with two red faces and one green face.
    • Second half: The two red faces are the larger faces from the cut, and they share edges with the two adjacent green faces. Similarly, this arrangement also results in 8 edge cubes with two red faces and one green face.
  3. Summing these, we find: 8+8=168 + 8 = 16

Conclusion

Thus, there are 16 cubes with two red faces and one green face.


Would you like further details, or have any questions about this solution?


Related Questions

  1. How many cubes have exactly three green faces?
  2. How many cubes have exactly one red and two green faces?
  3. What is the number of cubes that have all six faces unpainted?
  4. If the second half had one more red face, how would the number of cubes with two red and one green face change?
  5. How many cubes have exactly two green faces and no red faces?

Tip

To solve similar painted cube problems, always start by visualizing or drawing the coloring on each face after each cut.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Geometry
Combinatorics
Spatial Visualization

Formulas

None specific; relies on spatial reasoning and counting techniques

Theorems

None specific; solution involves geometric visualization and combinatorial counting

Suitable Grade Level

Grades 9-11