8楼Betty老豆
(随便逛逛)
发表于 2009-3-26 13:58
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A， Find the value.....
求和公式：=(2/9)*(1-1/(n+1)) n=2007/9, 所以结果是223/1008
B,Evaluate.......
同样求和：9+1+1/2-1/n-1/(n+1)， n=10, 所以结果是10+17/55
1. The product of n whole numbers 1 x 2 x 3 x 4 x 5 x …x (n-1) x n has twenty eight
consecutive zeros. Find the largest value of n.
乘到100是24个零了（有用的小常识），所以到120就有28个零了，n最大就是124
2. How many ways are there to distribute 28 identical marbles into 3 different boxes such
that no box is empty?
排列组合，计算C27 2 （上下标）就可以了，结果是351
3. Find the largest number n such that there is only one whole number k that satisfies
8/21 < n/(n+k) < 5/13
(Note: A<B<C means that value of B is between A and B)
转换：40/105<n/(n+k) < 40/104 = 80/210 <n/(n+k) < 80/208 即可知n=80 时，k=209-80=129，满足条件且k为唯一整数
4. Give that (200820082008…2008623) / (n of 2008), find the smallest value of n such that
the number is divisible by 11.
题目没看明白啊，汗，只知道要让11除尽，该数的偶数位加起来等于奇数位就行了。。。
中午匆忙一做，发现3题做反，改过，
[ 本帖最后由 Betty老豆 于 2009-3-26 14:46 编辑 ].
