作者xshane831 (Shane)
看板Grad-ProbAsk
标题Re: [问题] 离散请教
时间Thu Mar 19 21:26:46 2009
※ 引述《loeooo (篮球狂)》之铭言：
: 1. how many solutions are there to the equation X1+X2+X3+X4+X5=21,
: where Xi, i=1,2,3,4,5 is a nonnegative integer such that 0<=Xi<=10
: 求整数解个数跟求非负整数解个数一样吗? 求整数解我会
: 但求非负要怎麽求阿?
这是用生成函数解法 每个X的生成函数(1+X^1+X^2+...+X^10)
五个就是(1+X^1+...+X^10)^5 最後求X^21的系数
: 2. There are _________ consecutive 0s at the end of the binary expansion
: of 70!
: 3. there are ________4-digit decimal telephone numbers haviing one or
: more repeated digits.
: 4. if there are five possible grades, A,B,C,D,and F, the minimum number of
: students required in a class to be sure that at least six will receive the
: same grade is ________________.
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