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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 293

hi

If I have the 1 circle, 3 triangles and two hexagons and they're in a bag and pick them two times with return what is the probability of getting exactly one hexagon ?

I get 3/9 but the answer is 4/9....

help pls thanks

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 85,347

Hi;

4 / 9 is the correct answer.

**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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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 293

Could you explain me how you did it ? I get 12/36 and not 16/36....

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 85,347

Hi;

For school problems you should be using the simplest ideas, especially when you are stuck. Did you draw a tree?

**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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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 293

yes. and what do you mean by simplest ideas ?

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 85,347

You always have to get an answer. One way, or the other.

Let me show you how to draw the tree without drawing it:

This is your set of possibilities,

now the triangles and the circle we are not interested in so we give them the generic label of "other." Your set becomes,

the tree looks like this,

oh

ho

oo

hh

do you follow?

**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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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 293

ok...

explain this

oh

ho

oo

hh

*Last edited by Al-Allo (2013-03-29 11:48:30)*

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 85,347

Hi;

oh = ( 4 / 6 ) ( 2 / 6 )

ho = ( 2 / 6 ) ( 4 / 6 )

oo = who cares

hh = who cares

Can you finish that?

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 293

it gives 16/36

but i still don't understand the logic behind it how did you get those numbers ?ty

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 85,347

ho means I drew a hexagon and then something else. The probability of drawing a h is 2 / 6 because there are 2 of them out of the total 6. Then I draw an o, the probability is ( 4 / 6 ) because there are 4 of them out of 6. Same logic for oh.

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 293

i think im gonna re read the problem... im not sure of even understanding what they want ..ty for your help

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 85,347

If you are not sure of the problem then please just copy it over here.

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 293

Here :

An aleatory experience consists of turning an arrow on a roulette two times. (3 triangles, 1 circle, and two hexagon)

Question : What is the probability of obtaining exactly one haxagon.

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 85,347

The question is the same as the one you posted in post #1. The answer and logic are the same, 4 / 9. I can draw a tree if it will help.

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 293

Yes, please. !

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 85,347

Here is the full tree do you know what to do from here? Pay no attention to the numbers after the words circle triangle or hexagon.

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

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**Al-Allo****Member**- Registered: 2012-08-23
- Posts: 293

anyway, ill go through what you posted tomorrow, i dont have the energy tonight to think about it. thanks for your efforts to help.*curiously, when you get stuck on problems, how do you operate to solve them? any principles,etc. ?

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 85,347

For probability and combinatorics when stuck I do it the hard way. No calculations, draw trees or count them all by hand.

Of course that result can be rigorously obtained, but who cares?

Combinatorics is Algebra and Algebra is Combinatorics.

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