求教一道數(shù)學(xué)排列組合的題,
說九個字母POSSESSES被寫在9張不同的卡片上,然后從中隨機抽出四張卡片.
（1）問一共能抽出多少組不同的四張卡片.（組合）
（2）一共有多少種可能出現(xiàn)的四張卡片的排列.（排列）
可能說的不是很清楚,是一道英文題,原文如下.
The letters of the word POSSESSES are written on nine cards,one on each card.The cards are shuffled and four of them are selected and arranged in a straight line.
(a)How many possible selections are there of four letters?
(b)How many arrangements are there of four letters?
獎勵你五十分,前提條件是過程要清楚,要能讓我看明白.