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 Post subject: Help please - ProbabilityPosted: Fri Sep 19, 2008 8:25 pm

Joined: Fri Sep 19, 2008 8:19 pm
Posts: 3
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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 Post subject: Posted: Fri Sep 19, 2008 8:30 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13037
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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 Post subject: Posted: Fri Sep 19, 2008 8:45 pm

Joined: Fri Sep 19, 2008 8:19 pm
Posts: 3
Thank you so much, I would never have got that.

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 Post subject: probabiltyPosted: Fri Sep 19, 2008 10:20 pm

Joined: Wed May 09, 2007 2:09 pm
Posts: 915
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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 Post subject: Posted: Fri Sep 19, 2008 11:39 pm

Joined: Fri Sep 19, 2008 8:19 pm
Posts: 3
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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 Post subject: Re: Help please - ProbabilityPosted: Sat Sep 20, 2008 8:49 pm

Joined: Fri Jul 06, 2007 8:31 pm
Posts: 1245
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

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

_________________
Animis opibusque parati

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 Post subject: Posted: Sat Sep 20, 2008 9:14 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13037
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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