明天交功課

Do you mean how many methods can 2 different people pair up, or how many methods the 200 people can be arranged?

If the question is asking how ma ny methods 2 people can pair up, then it's just choosing 2 from 200 people = 200C2 = 200*199 / 2 = 19900

if it's how many methods 200 people can be arranged, then the answer is very big:
You can view it this way:
You choose 2 from 200, then choose 2 from remaining 198... (and it goes on and on) then 2 from remanining 2.
Moreover, each groups you choose are non-distinguishable, so you should divide it by 100!

Hence number of methods
= (200C2 * 198C2 * ...*2C2) / 100!
= 200! / (50! * 2^100 )

我覺得會咁計-.-但唔知岩唔岩
(1*199)*200
=39800

200 X 199 X 198 X 197.... X 3 X 2 X1=78865786736479050355236321393219 X 1之後 三十四個0

2007-03-25 22:54:59 補充：
Sry,是78865786736479050355236321393219 X 1之後 三百七十四個0

2007-03-25 23:00:02 補充：
SRY,全部錯誤，應是200 X 199/2

2007-03-25 23:00:59 補充：
=19900