有3个不懂的PREP数学题,请教大家,帮我看看,搞不好你也不会

做了下PREP破解版题库一的PS的100题就发现居然有3个不懂的,丢人的很啊...

特向大家请教下面3题

A certain law firm consists of 4 senior partners and 6 junior partners.  How many different groups of 3 partners can be formed in which at least one member of the group is a senior partner?  (Two groups are considered different if at least one group member is different.)

(A) 48

(B) 100

(C) 120

(D) 288

(E) 600

我选的D, 至少一个是 S , 其他的就随便了,不就是: C4-1乘以C9-1再乘以C8-1吗?

先从4个S中选一个,剩下的9个人中再选一个,再从剩的8个中选一个,如此以来,是288,但答案是E,不懂...

If x^4 + y^4 = 100, then the greatest possible value of x is between

(A) 0 and 3

(B) 3 and 6

(C) 6 and 9

(D) 9 and 12

(E) 12 and 15

答案是B,我选的A,因为4的4次方已经是256了,更别说5的4次方,6的了,而3的3次方81,

所以X更可能落在0和3之间,我不知道我怎么错了,郁闷.

In a certain deck of cards, each card has a positive integer written on it.  In a multiplication game, a child draws a card and multiplies the integer on the card by the next larger integer.  If each possible product is between 15 and 200, then the least and greatest integers on the cards could be

(A) 3 and 15

(B) 3 and 20

(C) 4 and 13

(D) 4 and 14

(E) 5 and 14

选C,我没看懂题目什么意思,If each possible product is between 15 and 200,那15不是有3这个元素吗? 所以最小肯定有3啊... 我没弄懂请教大家...

哦，谢谢楼上...我问题没有看明白...

greatest possible value 是可能的最大值,而不是值可能落在哪里...

第一題確實是600

P(10,3)-P(6,3)=720-120=600

因為每一個senior partner跟junior partnet都不一樣

这个解释我认为可能有点问题，因为只要选就行了，不需要排的, 比如选了两个senior, 哪个先选,哪个后选,无所谓的...

所以我还是认为这个式子是最好:C10-3减C6-3是最简洁而明郎的,所有的可能出现组合减去不合条件的组合

谢谢大家,下午几个问题一会就全懂了,感谢大家