3道gmat 数学概率排列组合题

3道gmat 数学概率排列组合题
1.On a certain transatlantic crossing,20 percent of a ship’s passengers held round-trip tickets and also took their cars abroad the ship.If 60 percent of the passengers with round-trip tickets did not take their cars abroad the ship,what percent of the ship’s passengers held round-trip tickets?A.33 1/3% B.40% C.50% D.60% E.66 2/3% 2.There are 8 books on a shelf,of which 2 are paperbacks and 6 are hardbacks.How many possible selections of 4 books from this self include at least one paperback?A.40 B.45 C.50 D.55 E.60 3.There are 8 magazines lying on a table; 4 are fashion magazines and the other 4 are sports magazines.If 3 magazines are to be selected at random from the 8 magazines,what is the probability that at least one of the fashion magazines will be selected?A.1/2 B.2/3 C.32/35 D.11/12 E.13/14 求指教 和具体解法 已晕= =