Question

A school bus has 25 seats, with 5 rows of 5 seats. 15 students from the first grade and 5 students from the second grade travel in the bus. How many ways can the students be seated if all of the second-grade students occupy the first row?

25P20
5P5 × 20P15
5C5 × 25C14
5P5 × 15P15
5P5 × 25C15

Answer 1

Option B is correct

Explanation:

B. 5P5 × 20P15

Answer 2

First row: permutation of 5 seats taken 5 (second grade students) at a time (second grade students) => 5P5

Other 4 rows: permutation of 20 seats taken 15 (first grade students) at a time => 20P15

Total different ways: 5P5 * 20P15