Permutation and combination problem. High school math. Find out the detailed problem-solving process.
Answer: The number of rectangles is 7, 2 vertical, 5, 2 horizontal, and then multiply.
That is, C7 takes 2 times C5 takes 2.
That is, 2 1× 10=2 10 different rectangles,
The shortest route can be divided into six segments and take five different roads, that is, six 1, six 2, ... six 6 plus five, that is, C30 takes five.