permutation and combination

4. b)

In the first, third, fifth and seventh rows, there are totally 16 seats.
Number of ways to arrange the 16 girls to take the 16 seats = 16P16

In the second, fourth, sixth and eighth rows, there are totally 20 seats.
Number of ways to arrange the 16 boys to take the 20 seats = 20P16

Number of ways to arrange the students' seats
= 16P16 x 20P16
= 16! x (20!/4!)
= 2120962397298879029575680000000

answer for a should not be 36C32 , should be 36P32?

2012-11-13 13:21:17 補充：
if 36C32, then ABCD=ABDC=ACBD=ACDB=...!
it should not be true in real life!

Just consider single column, if there are 5 seats and 4 students only
seat arrangement should be 5P4, not 5C4

it should be permutation since AB and BA are different ways!!!