我也用了超過五分鍾，主要是"要檢票前若幹分鍾就開始排隊"...

這句話一開始沒理解好。如果理解了開始檢票前，旅客的增長率也是常數，那題目就很容易了。

y = rate of passenger growth (person/minute)
x = number of minutes the line had been forming BEFORE admission starts
z = rate of admission
A = how long it takes with 8 windows(answer)

y*(x+40) = 3*40*z ==> x+40 = 120*(z/y)
y*(x+25) = 4*25*z ==> x+25 = 100*(z/y)

(z/y) can be treated as one variable here, so this is easily solved to get the two variables x and (z/y), then just solve:
y(x+A) = 8*A*z ==> x+A = 8*A*(z/y)
to get A

so 處方 was right, 10 minutes

所有跟帖： 

• 啥問題？家有奧數少年的俺，木油看出來。。。 -Yuan- ♀ (0 bytes) () 02/16/2009 postreply 16:13:05

• 排在隊裏滴=被processed滴，總不總的不知道，是個動態的處理工作 -Yuan- ♀ (0 bytes) () 02/16/2009 postreply 18:01:56