GRE
$$\frac{100!}{99!}$$
$$\frac{ (100!-99!)}{98!}$$
$$\frac{(5!+6!)}{(6!+7!)}$$
$$\frac{1}{6}$$
20!+19!+18!
400(18!)
$$\frac{23!}{(11!*13!)}$$
$$\frac{23!}{(10!*14!)}$$
$$\frac{n!}{(\frac{n}{2})!}$$
2($$\frac{n}{2}$$)!
The probability that the number selected will have a units digit of 6
The probability that the number selected will have a tens digit of 6
The number of ordered pairs (x, y) in S such that x=y
16
The number of ordered triples ($$x_1$$, $$x_2$$, $$x_3$$), where $$x_1$$, $$x_2$$ and $$x_3$$ are non-negative integers such that $$x_1$$+$$x_2$$+$$x_3=9$$
$$55$$
25000 +道题目
252本备考书籍
