This problem comes from the teaching design of the first volume of primary school mathematics, Understanding Three-dimensional Graphics, which is a high-quality open class. Numbering method: 7 on the first floor, 7+5= 12 on the second floor, 12+3= 15 on the third floor, and15+16 on the fourth floor.

In mathematics, a small cube usually means a cube surrounded by six squares. In a more specific definition, a small cube is a special three-dimensional figure, and all six small squares have the same area. Each face of this small cube can be covered by the same square.

Cube is an important concept in primary school mathematics, which is often used to help pupils better understand the concept and properties of solid geometry. For example, the three-dimensional figure obtained by translating the side length of a square in the direction perpendicular to the plane of the square is a small cube.

Skills of counting small cubes:

1. Understanding rules: Before solving any math problem, understand the rules and conditions given by the problem. For counting small cubes, you need to know the key factors such as the arrangement, color and size of cubes.

2. Hierarchical solution: An effective strategy is to solve problems involving 3D arrays hierarchically. You can start at the bottom and work your way up, which will make the problem easier to deal with.

3. Marking method: For more complex arrays, you may find it necessary to use marking method or symbology to track different cubes. For example, you can use a specific symbol or color to represent a layer's cube.

4. Use the model: Sometimes, using the model can help to understand the problem. You can use building blocks or similar tools to simulate the array and find out the answer through intuitive observation.

5. Pay attention to details: When solving such problems, you must be careful and don't miss any details. Check the calculation of each step to ensure that there are no mistakes or omissions.

6. Use logic: Most of these problems can be solved by logical reasoning. Use your logical thinking to try to find out the law behind the problem.

7. Practice: Improve problem-solving skills through a lot of practice. Try to solve different types of problems and gradually accumulate experience.

8. Check the answer: After completing the question, check whether the answer meets your expectations. If the answer is unreasonable, it may be that you made a mistake in solving the problem.

9. Sum up experience: After each problem is solved, sum up how you found the answer and think about whether there is a better way. This will help you better understand the problem and improve the speed of solving it.