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?
Number of ways the second grade students can sit on the first row is 5! = 5P5 Number of ways 15 first grade students can sit in the remaining 20 seats is 20P15
Therefore, required number of ways is 5P5 * 20P15. (option B)
