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

All the 15 first first grade students want to sit in the first 15 seats....so no. of ways if permuting them is 15! followed by 
the remaining 5 students have a total of 10 seats...so total no. of ways of permuting 5 students in 10 seats in 10P5... 
So, 15P15 x 10P5