For example: 0, 5, 8 to match two numbers, you can teach children to fix one number in ten numbers first, and then match the other two numbers in one number. The interesting thing about this question is that 0 can't be placed in the tenth place, so you can only put 5 in the tenth place to form two numbers 50 and 58; Then put 8 in the tenth place to form two numbers, 80 and 85. Finally, the answer is four numbers: 50, 58, 80, 85.
Matters needing attention
Unit 8 of the first volume of the second grade mathematics discusses the "collocation problem" from a wider angle, which is very important. The simple arrangement and combination of second-grade learning is not only versatile, but also a good material for training students' abstract ability and logical thinking ability.
There is a learning difficulty here, that is, how to arrange it, without repetition or omission. This requires students to observe carefully, use their hands and brains, do more exercises, verify the thinking of solving problems and accumulate experience in the process of solving problems.