急 ! 排列與組合次方問題

有4個區域，每一個區域都填上綠色，藍色，黃色或紅色的其中一色，求至少
一個區域為紅色.
Sol
N(至少1個區域為紅色)
=N(所有方法)－N(沒有1個區域為紅色)
=4^4－3^4
沒有1個區域為紅色=>只能填上綠色，藍色，黃色共3色的其中一色

on this problem,you should concern that whether the problem is conditional probability(條件性概率),the conditional probability will have a evident relationship.you can viewing this website(http://dufu.math.ncu.edu.tw/calculus/calculus_eng/node215.html) to learn what is conditional probability.

in your solution ,this method is not the conditional probability,but 4^4-4^3 is running the conditional probability.

i hope i can solve your question