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**samuel baffoe****Member**- Registered: 2010-08-25
- Posts: 5

1) A man is given n keys, in random order of which only one will unlock his door. He tries them one by one (without replacement). find P(man succeeds on k*th trial)

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,257

Hi Sam;

A question for you, you have posted several other questions.

I don't know whether or not you needed help or you were just posing a problem.

I answered them, can you check them and tell me what you think?

**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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**noemi1982****Member**- Registered: 2010-12-11
- Posts: 5

una clase consta de 14 hombres y de 30 mujeres de los cuales la mitad de los hombres y la mitad de las mujeres usan anteojos. Hallar la probabilidad de que una persona escogida al azar 1) sea hombre 2) use anteojos 3) sea hombre y use anteojos.

probabilidad por medio de Laplace

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**noemi1982****Member**- Registered: 2010-12-11
- Posts: 5

en un experimento se tira 4 veces seguida una ficha de 2 caras, una roja y la otra blanca. calcular la probabilidad de:

1/ obtener exactamente una cara roja

2/ por lo menos una cara roja

3/ ninguna cara roja. hacer el conteo de los casos

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,257

Hi noemi1982;

noemi1982 wrote:

una clase consta de 14 hombres y de 30 mujeres de los cuales la mitad de los hombres y la mitad de las mujeres usan anteojos. Hallar la probabilidad de que una persona escogida al azar 1) sea hombre 2) use anteojos 3) sea hombre y use anteojos.

probabilidad por medio de Laplace

Welcome to the forum! I do not understand what you mean by the method of Laplace.

Here are my answers:

1) P( is a man ) = 14 / 44

2) P(wears spectacles) = 1 / 2

3) P( is a man and uses spectacles ) = 7 / 44

**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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**noemi1982****Member**- Registered: 2010-12-11
- Posts: 5

regla de Laplace: se aplica cuando los "n" resultados son equiprobables.

P(A)= numero de caso favorable / numero de casos posibles

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,257

Hi;

I understand. Then my answers in post 5 are correct, if I am translating correctly. I hope so.

I use P = successes / ( successes + failures ).

**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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**noemi1982****Member**- Registered: 2010-12-11
- Posts: 5

en un experimento se tira 4 veces seguida una ficha de 2 caras, una roja y la otra blanca. calcular la probabilidad de:

1/ obtener exactamente una cara roja

2/ por lo menos una cara roja

3/ ninguna cara roja. hacer el conteo de los casos

thank

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,257

Hi;

I am sorry, I was able to understand your other posts because I had my brother to help translate. I do not understand spanish as well as he does. I think you are saying you flip a card 4 times and one side is red and the other side is white? Am I close?

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

Combinatorics is Algebra and Algebra is Combinatorics.

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**noemi1982****Member**- Registered: 2010-12-11
- Posts: 5

In an experiment if you throw a double faced chip four times in a row with one face red and the other white.

Calculate the probability of:

1/exactly getting a red face

2/getting at least one red face

3/get no red faces

account the cases.

thanks

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 86,257

Hi noemi1982;

Thanks for translating for me. I am learning a little spanish but I am a slow learner. I am going to assume that the probabilities of either face are equal.Okay we have a binomial experiment.

1) P(getting 1 red face) = 1 / 4

2) P(getting at least 1 red face) = 15 / 16

3) P(getting 0 red faces) = 1 / 16

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

Combinatorics is Algebra and Algebra is Combinatorics.

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