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Deon588

Member

Registered: 2011-05-02

Posts: 68

Probability question which seems a bit unreasonable

Hi all.  I can't think that I would get a question like this if i'm understanding this correctly
Question:  There are 5 50c coins and 3 20c coins in a tin label the 50c coins f_1 to f_5 and the 20c coins t_1 to t_3.  suppose you put your hand in the tin and take out 3 coins without looking.  Write down the set that represents the event "I have at least one 50c coin amongst the 3 coins that I drew"

Deon588

Member

Registered: 2011-05-02

Posts: 68

Re: Probability question which seems a bit unreasonable

I don't think I was totally clear.  So my problem is.  It seems like that would be a very big set?  And not something I would be expected to do in a exam?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,155

Re: Probability question which seems a bit unreasonable

hi Deon588,

If the 50c were just labelled F (all five of them) and the 20c similarly labelled T, then it wouldn't be so bad.  I agree with you that writing all the possibilities using f_1 etc would make a long list.

If all eight coins are distinct and order is not relevant, then there are (8 x 7 x 6) /(3 x 2 x 1) = 56 ways of listing them all.  So if you reduce this list to exclude any which have no 50c coins ... how many is that?  Must be 56 - 1 = 55.

Did this come out of a book or from a teacher?  If the latter, go and check.

I don't think it would come up in an exam.

Bob

Last edited by Bob (2011-10-02 20:01:20)

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Children are not defined by school ...........The Fonz
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Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Deon588

Member

Registered: 2011-05-02

Posts: 68

Re: Probability question which seems a bit unreasonable

Hi Bob good to know i'm understanding this correctly...  This came from revision exercises my lecturer created so i'll have to check with her