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  Discussion about math, puzzles, games and fun.   Useful symbols: √ ∞ ≠ ≤ ≥ ≈ ⇒ ∈ Δ θ ∴ ∑ ∫ π -

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#1 2013-01-22 04:13:22

cooljackiec
Full Member

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probability and counting??

How many 20-digit numbers are such that the sum of their digits is even?


I see you have graph paper.
You must be plotting something
lol

#2 2013-01-22 05:42:14

muxdemux
Full Member

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Re: probability and counting??

I could only figure out that there's at least

.

Last edited by muxdemux (2013-01-22 05:42:30)

#3 2013-01-22 08:25:37

cooljackiec
Full Member

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Re: probability and counting??

That doesn't help, I knew that just that i keep losing count.


I see you have graph paper.
You must be plotting something
lol

#4 2013-01-22 12:24:26

bobbym
Administrator

Online

Re: probability and counting??

Hi;

You do not have to do much counting. Spot the pattern works well here.

I am getting 4.5 x 10 ^19 numbers.


In mathematics, you don't understand things. You just get used to them.
I have the result, but I do not yet know how to get it.
All physicists, and a good many quite respectable mathematicians are contemptuous about proof.

#5 2013-01-23 11:02:13

cooljackiec
Full Member

Offline

Re: probability and counting??

Thank you


I see you have graph paper.
You must be plotting something
lol

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