b***k
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bluegene (蓝色基因||多看paper才是王道) 于 (Sat Mar 22 01:17:46 2008) 提到:
there is a menu of 5 different kinds of donut and you want to buy 3 donuts,
how many ways can you do it?
it is not hard to figure out that the answer is 5*6*7/(3*2*1),
but how to rationalize this answer?
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woodknife (小木飞刀) 于 (Sat Mar 22 01:36:06 2008) 提到:
four stickss, separating a line into five pieces, and each part represents
one kind of donut. |
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