8 letter send to 3 places
no.of ways:3^8
if each places at least recieve 1 letter , no of ways : 3^8 - ?
combination
2011-12-23 4:03 am
回答 (1)
2011-12-23 4:48 am
✔ 最佳答案
The required ways= All ways - only 2 places recieve letter ways - only 1 place recieve letter ways= 3⁸ - (3C2) * (2⁸ - (2C1)*1⁸) - (3C1) * 1⁸= 6561 - 3 * (256 - 2) - 3= 5796 ways
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