Math Is Fun Forum

cooljackiec

Member

Registered: 2012-12-13

Posts: 186

probability and counting??

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

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

muxdemux

Member

Registered: 2012-12-23

Posts: 80

Re: probability and counting??

I could only figure out that there's at least

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

cooljackiec

Member

Registered: 2012-12-13

Posts: 186

Re: probability and counting??

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

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

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

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.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

cooljackiec

Member

Registered: 2012-12-13

Posts: 186

Re: probability and counting??

Thank you

---

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