Introduction to Combinatorics Chapter 1 Answers 20-28_Introduction to Combinatorics Sun Shuling Answers Chapter 1_wjk20120522’s blog

20. Solution: The idea is similar to Example 3 in Section 1.2, but there is one step more than Example 3.

26. Solution: The simple application of the pigeonhole principle, the remainder 0…n-1.n+1 takes the n numbers 0..n-1, there must be two numbers with the same remainder, and it is proved.

27. Solution: The idea is similar to the fourth question

28. Prove that the sum of the x, y, and z coordinates of the three points is an even number. Similar to Example 3 in Section 1.2.