Q1：
(i) six defence players are chosen from twenty five hockey players,the possible is C(25,6),then,five forward players are chosen from the other nineteen ,possible is C(19,5)；
so,there can be C(25,6)*C(19,5) teams;
(ii) six defence players are chosen from the ten available,the possible is C(10,6),and,five forward players are chosen from the fifteen available,possible is C(15,5)；
so,there can be C(10,6)*C(15,5) teams
Q2:
(i) As Seventy percent of the first-year students are male,there are
12(40*30%) students are female from 40 first-year students. and seven of the female students graduated from high school the year before,so 5(12-7)female students took a “gap-year”；
To conclude, the probability is 1/8（5/40）that a randomly selected first-year student is both female and took a “gap-year”.
（ii）The probability is 1/2（half of 40）that given a randomly selected from 40 first-year students are “gap-year”ones, and the probability is 3/8[（1/2）*（15/20）]that given a randomly selected 40 first-year studes are male from “gap-year”ones.
So, the probability is 3/4 [（3/8）/（1/2）]that given a randomly selected student took a “gap-year” the student is male.
Q3：
(i) there are 22（13+12-3） red cards or face cards,so the probability is 11/27（22/54） that the card drawn is a red card or a face card.
（ii）the probability of having only odd numbers result when an unbiased six-sided die is rolled one time is 1/2（3/6）；
when an unbiased six-sided die is rolled five times, the probability of having only odd numbers result is 1/32（1/2*1/2*1/2*1/2*1/2）.