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 Post subject: Probability question....Posted: Sun Jul 08, 2012 1:48 pm

Joined: Tue Mar 08, 2011 9:16 am
Posts: 686
Would really like to understand this one....

For which of these can you work out the probability exactly?

A) It will rain tomorrow when class B go on a school trip.
B) Mr. Wood will pass his driving test
C) Stuart will miss the 8.30 am bus to school
D) Emily will throw heads when she tosses a coin
E) Amy will come third in a swimming competition

?????

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 Post subject: Re: Probability question....Posted: Sun Jul 08, 2012 1:52 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 11932
D is the only one where the outcomes are equally likely.

Two outomes Head or tail - probability of a Head is 1/2.

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 Post subject: Re: Probability question....Posted: Sun Jul 08, 2012 1:56 pm

Joined: Tue Mar 08, 2011 9:16 am
Posts: 686
Guest55 wrote:
D is the only one where the outcomes are equally likely.

Two outomes Head or tail - probability of a Head is 1/2.

Thanks Guest55
What about passing/failing driving test isn't that 1/2 ( pass or fail )
Is this a straight forward one, have really struggled on it....

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 Post subject: Re: Probability question....Posted: Sun Jul 08, 2012 2:07 pm

Joined: Wed Mar 09, 2011 2:22 pm
Posts: 710
countrymum wrote:

B) Mr. Wood will pass his driving test

D) Emily will throw heads when she tosses a coin

Both these are 50/50

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 Post subject: Re: Probability question....Posted: Sun Jul 08, 2012 2:17 pm

Joined: Fri Sep 15, 2006 8:51 am
Posts: 8112
I think that for the probability to be calculated you have to know that each outcome is equally likely . heads or tails is equally likely but passing or failing a test may not be equally likely

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 Post subject: Re: Probability question....Posted: Sun Jul 08, 2012 2:18 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 11932
Passing and failing a driving test are not equally likely - I think it varies from test centre to test centre and a driver could be appalling.

Theoretical probability only applies where 'skill' is not part of the picture - spinning a coin, throwing a die, etc.

Playing football depends on the teams playing - the weather depends on the time of year and the country.

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 Post subject: Re: Probability question....Posted: Sun Jul 08, 2012 2:19 pm

Joined: Thu Nov 12, 2009 1:36 pm
Posts: 192
Location: East Kent
Manana wrote:
countrymum wrote:

B) Mr. Wood will pass his driving test

D) Emily will throw heads when she tosses a coin

Both these are 50/50

I guess someone is only likely to take their driving test if they think the odds are they are likely to pass - a coin toss has no element of skill (in that practice can have any outcome on the result you are likely to get)

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 Post subject: Re: Probability question....Posted: Sun Jul 08, 2012 2:27 pm

Joined: Tue Mar 08, 2011 9:16 am
Posts: 686
Guest55 wrote:
Passing and failing a driving test are not equally likely - I think it varies from test centre to test centre and a driver could be appalling.

Theoretical probability only applies where 'skill' is not part of the picture - spinning a coin, throwing a die, etc.

Playing football depends on the teams playing - the weather depends on the time of year and the country.

Thanks everyone and guest55, thanks so much for that. It has all clicked and I get it now! Kind of thinking out of the box and taking many outside influences into account ( like for eg the weatherman mayhave got it wrong or like you say he may a rubbish driver etc etc )

Yes the answer is indeed D! If I get stuck again can I come back
You are all masters of maths

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 Post subject: Re: Probability question....Posted: Sun Jul 08, 2012 2:49 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 11932
I should hope so as I spend my life teaching it!

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