Senior three math problems (detailed answers)

Test analysis: 3 boys and 3 girls stand in two rows, and 3 people in each row take a group photo. There are 720 kinds of standing postures, 72 of which are aimed at three boys in the same row, so there are 648 kinds of standing postures for three boys who don't stand in the same row, so C.

In addition, extracurricular knowledge extension:

Arrangement:

1, the concept of arrangement: take out m(m≤n) elements from n different elements and arrange them in a certain order, which is called the arrangement of taking out m elements from n different elements. ?

2. Complete arrangement: The arrangement in which all N different elements are taken out is called the complete arrangement of these N elements. ?

3. The concept of permutation number: the permutation number of m(m≤n) elements from n different elements is called the permutation number of m elements from n different elements.

4. factorial: the product of natural number 1 pair n, where n! = 1× 2× 3× ...× n？

Regulation: 0! = 1?

Combination:

1, the concept of combination: taking out m elements from n different elements and grouping them is called taking out the combination of m elements from n different elements. ?

2. Concept of combination number: The number of all combinations of M elements taken from N different elements is called the combination number of M elements taken from N different elements.