How many positive numbers smaller than 10^n such that their digits are non-decreasing from left to right (e.g.?
2009-11-13 3:49 pm
How many positive numbers smaller than 10^n such that their digits are non-decreasing from left to right (e.g. 233344589)?
回答 (2)
2009-11-13 4:57 pm
✔ 最佳答案
answer= [(n + 9)! / n!9!] - 1
= C(n+9,n) - 1
2009-11-14 12:13 am
Solution write 9 for n times
Example
10^1; n=1 ; there are 9 positive numbers smaller than 10^1
10^4; n=4 ; there are 9999 positive numbers smaller than 10^4
Good luck!
Example
10^1; n=1 ; there are 9 positive numbers smaller than 10^1
10^4; n=4 ; there are 9999 positive numbers smaller than 10^4
Good luck!
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