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PostPosted: Fri Sep 19, 2008 8:25 pm 
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Joined: Fri Sep 19, 2008 8:19 pm
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Can anyone help me with this question please?

Siobhan has 0.8 chance of passing English GCSE, and a 0.6 chance of passing Maths GCSE. What is the probability that she will pass either English or Maths?

Thank you


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PostPosted: Fri Sep 19, 2008 8:30 pm 
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If passing English is 0.8 then failing will be 0.2 so:

Fails English and passes Maths = 0.2 x 0.6 = 0.12

Passes English and fails Maths = 0.8 x 0.4 = 0.32

so passing only one = 0.44

[passing both = 0.8 x 0.6 = 0.48]


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PostPosted: Fri Sep 19, 2008 8:45 pm 
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Thank you so much, I would never have got that. :)


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 Post subject: probabilty
PostPosted: Fri Sep 19, 2008 10:20 pm 
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Location: Solihull, West Midlands
This doesn't seem a very well worded question - are they looking for the probability that she passes at least one of English & maths (which would be 0.92 or 1-(prob she fails both = 0.08) or the probability she passes only one or the other but not both (which is 0.44 as shown by Guest55)


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PostPosted: Fri Sep 19, 2008 11:39 pm 
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I agree, it is badly worded. I'm not sure which they are looking for, but since I didn't know the answer to either possibilities, both your help has been appreciated.


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PostPosted: Sat Sep 20, 2008 8:49 pm 
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Joined: Fri Jul 06, 2007 8:31 pm
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Nikki wrote:
Can anyone help me with this question please?

Siobhan has 0.8 chance of passing English GCSE, and a 0.6 chance of passing Maths GCSE. What is the probability that she will pass either English or Maths?

Thank you


Here's my answer...

This is 1 - p(failing both)

p(fail english) = 1-0.8 = 0.2
p(fail math) = 1-0.6 = 0.4

p(fail both) = 0.2 x 0.4 = 0.08

p(pass one of other) = 1-0.08 = 0.92

92% chance of passing one or other

Regards
SVE

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PostPosted: Sat Sep 20, 2008 9:14 pm 
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Joined: Mon Feb 12, 2007 1:21 pm
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It is badly worded.

It should say 'find the probability of passing only one of English or Maths' or 'find the probability of passing English or Maths or both'.


It is not clear what is required - is this really from a 11+ paper?


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