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**cooljackiec****Member**- Registered: 2012-12-13
- Posts: 160

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

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**muxdemux****Member**- Registered: 2012-12-23
- Posts: 80

I could only figure out that there's at least

.*Last edited by muxdemux (2013-01-21 06:42:30)*

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**cooljackiec****Member**- Registered: 2012-12-13
- Posts: 160

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

I see you have graph paper.

You must be plotting something

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,366

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.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

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**cooljackiec****Member**- Registered: 2012-12-13
- Posts: 160

Thank you

I see you have graph paper.

You must be plotting something

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