Math Is Fun Forum

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

natur numb div 3, prob div 9

If a natural
number is
divisible by
3, what is
the probability
it is divisible
by 9 ?

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igloo myrtilles fourmis

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: natur numb div 3, prob div 9

Hi John E. Franklin;

I am going with 1 / 3.

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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.

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: natur numb div 3, prob div 9

Yup, that's what my
girlfriend just said too
on the phone.  Took
her about 2 1/2 seconds
to get it.  It took me
more like 30 seconds.

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igloo myrtilles fourmis

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: natur numb div 3, prob div 9

Hi;

Then ask her this question. What is the probability of a natural number being divisible by 3. She will say 1 / 3. What is the probability that it is not, she will say 2 / 3. Since the set of natural numbers that are divisible by 3 has a probability of 1 / 3 it should be smaller than the set of natural numbers. Is that correct?

---

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.

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: natur numb div 3, prob div 9

Yes, we have already talked about infinity together a bit, and
I'm sure she would get that right in an instant, she has a
masters degree in mathematics!

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igloo myrtilles fourmis

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: natur numb div 3, prob div 9

I am sure also. Wasn't trying to imply it would stump her, just thought if you needed something to say.

---

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.