gwd26-33

[邁向高等學府]

The figure above represents a system of roads along which traffic flows in the direction indicated by the arrows. If the traffic were to split everly at each fork ot the road system, what percent of the traffic entering forc C wyould exit at Y?

a. 87.5%
b. 75%
c. 62.5%
d. 50%
e 12.5%

Ans: A

怎麼算滴…我不會…煩請站上大大解答…
P.S.圖我不會貼…不好意思…

[hey]

這一題是說從C進去而從Y出來的機率有多高...
這一題用反向思考會比較快... 就是將從C進去而從X出來的機率減掉...
1-(1/2*1/2*1/2)=87.5%
至於1/2是怎麼來的呢? 因為第一個路口分岔為2, 那麼每一個路口的機率會為1/2囉, 第二個路口又分岔為2, 所以機率又是1/2, 第三個路口還是分岔為2, 機率還是1/2, 如果一直沿著C往路口X走的話, 則為1/2*1/2*1/2
但此題是算往Y出來的機率, 所以就用1去減掉往X出去的機率, 就會得到(A)這個答案囉