Answer:
The correct option is b.
Step-by-step explanation:
It is given that the school bus has 25 seats, with 5 rows of 5 seats.
The number of students from the first grade is 15 and the number students from the second grade is 5.
The formula to arrange r items in n places is
[tex]^nP_r=\frac{n!}{(n-r)!}[/tex]
The number of seats in first row is 5 and the number students from the second grade is 5. So, the total number of arrangement is
[tex]^5P_5[/tex]
The number of seats except first row is 20 and the number students from the first grade is 15. So, the total number of arrangement is
[tex]^{20}P_{15}[/tex]
The total number of ways the students can be seated if all of the second-grade students occupy the first row is
[tex]^5P_5\times ^{20}P_{15}[/tex]
Therefore the correct option is b.
