The grouping process is as follows:
1. Considering that the packet must contain "1" and "2", it is necessary to select the third number from the remaining three numbers for combination.
Then the third number can be "3" or "4" or "5".
That is, the grouping is "123", "124" and "125".
2. Considering that the grouping must contain "1" and "3", it is necessary to select the third number from the remaining two numbers for combination.
Then, the third number can be "4" or "5". ("2" cannot be selected because "123" has been considered in the first case)
That is, the grouping is "134" and "135".
3. Considering that the packet must contain "1" and "4", it can only be combined with the remaining 1 numbers.
That is, the grouping is "145". ("2" and "3" cannot be selected, and the first and second cases have been considered)
4. Considering that the grouping must contain "2" and "3", it is necessary to select the third number from the remaining two numbers for combination.
Then, the third number can be "4" or "5". ("1" cannot be selected because "123" has been considered in the first case).
That is, the grouped groups are "234" and "235".
5. Considering that the packet must contain "2" and "4", it can only be combined with the remaining 1 digits.
The grouping that can be formed is "245". ("1" and "3" cannot be selected, and the first and fourth cases have been considered)
6. Considering that the packet must contain "3" and "4", it can only be combined with the remaining 1 digits.
The grouping that can be formed is "345". ("1" and "2" cannot be selected, and the second and fourth cases have been considered)
So a * * * can be divided into ten groups, namely: 123, 124, 125, 134, 135, 145, 234, 234.
This problem is essentially a "combination" problem in mathematics.
Extended data
The nature of the combination:
Combination is one of the important concepts in mathematics. Taking out M different elements (0≤m≤n) from N different elements at a time and synthesizing a group regardless of their order is called selecting the combination of M elements from N elements without repetition. The sum of all these combinations is called the number of combinations.
References:
Baidu Encyclopedia _ Combination (Mathematical Noun)