Problem 1. A paper rectangle $3 \times 7$ was cut into squares $1 \times 1$. Each square, except those that stood at the corners of the rectangle, was cut along both diagonals. How many small triangles were obtained?
Answer: 68.

Solution. Note that the total number of squares cut along the diagonals is $3 \cdot 7-4=17$. Each of them is cut into 4 small triangles. Therefore, there will be $4 \cdot 17$ - 68 small triangles.