This problem is similar to Coupan collector problem.
http://en.wikipedia.org/wiki/Coupon_collector%27s_problem
In your case the answer is
[image: For N-Dice ; \newline \sum_{i=1}^{N} N/i \newline for\; N =~2 ;
\newline \sum_{i=1}^{2} 2/i = 2/1 + 2/2 = 3 \newline]
Hope it helps!
--
Amitesh
On Sat, Jun 16, 2012 at 5:18 PM, Gaurav Popli <[email protected]>wrote:
> What is the expected number of throws of his die while it has N sides
> so that each number is rolled at least once?
> e.g
> for n=2 ans 3.00
> n=12 ans is 37.24...
> i refrd to expectation tutuorial at
> http://www.codechef.com/wiki/tutorial-expectation but still couldnt
> get the logic...
>
> any help?
>
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