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Consider that the 4th person chose dish X.

The Probability that the 1st Person chose dish X is 1/5.

The Probability that the 2nd Person chose dish X is 1/5.

The Probability that the 3rd Person chose dish X is 1/5.

Therefore, the probability that anyone has chosen X before is 3/5.

So, the possibility that the dish is previously not chosen is 2/5

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

'You have made another human being happy. There is no greater accomplishment.' -bobbym

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 87,258

Is that the exact question?

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

Combinatorics is Algebra and Algebra is Combinatorics.

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I would say yes, because the answer you gave me works

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

'You have made another human being happy. There is no greater accomplishment.' -bobbym

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,428

Agnishom wrote:

The Probability that the 1st Person chose dish X is 1/5.

The Probability that the 2nd Person chose dish X is 1/5.

The Probability that the 3rd Person chose dish X is 1/5.

Therefore, the probability that anyone has chosen X before is 3/5.

That method is faulty. If there were 5 people before D, you would end up with 5/5 and no chance for D.

I'll work on an analytic method.

Bob

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 87,258

Must be different for me and you then. Mine requests a + b in a / b.

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

Combinatorics is Algebra and Algebra is Combinatorics.

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bob bundy wrote:

Agnishom wrote:The Probability that the 1st Person chose dish X is 1/5.

The Probability that the 2nd Person chose dish X is 1/5.

The Probability that the 3rd Person chose dish X is 1/5.

Therefore, the probability that anyone has chosen X before is 3/5.That method is faulty. If there were 5 people before D, you would end up with 5/5 and no chance for D.

I'll work on an analytic method.

Bob

Ya, so... What to do?

Hi bobbym,

They ask me for a + b too

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

'You have made another human being happy. There is no greater accomplishment.' -bobbym

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 87,258

You can not add them up.

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

Combinatorics is Algebra and Algebra is Combinatorics.

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Then?

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

'You have made another human being happy. There is no greater accomplishment.' -bobbym

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 87,258

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

Combinatorics is Algebra and Algebra is Combinatorics.

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,428

hi

I get that too by my own method and a general formula too.

Bob

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THanks

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

'You have made another human being happy. There is no greater accomplishment.' -bobbym

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