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 the first-grade students occupy the first 3 rows?

Question

anonymous · Answer

the first grade students can be seated in 15! ways 
and after that the second grade students can be seated in 25*24*23*22*21 ways
hence required no. of ways 
15! *(25*24*23*22*21)