A paper rectangle 3×7 was cut into squares 1×1. Each square, except those that stood at the corners of the rectangle, was cut along both diagonals. How many small triangles were obtained?
A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.
Solution. Note that the total number of squares cut along the diagonals is 3⋅7−4=17. Each of them is cut into 4 small triangles. Therefore, there will be 4⋅17 - 68 small triangles.
Source: NuminaMath-1.5,
licensed Apache-2.0.
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