Help please - Probability

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Nikki
Posts: 3
Joined: Fri Sep 19, 2008 9:19 pm

Help please - Probability

Post by Nikki »

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
Guest55
Posts: 16254
Joined: Mon Feb 12, 2007 2:21 pm

Post by Guest55 »

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]
Nikki
Posts: 3
Joined: Fri Sep 19, 2008 9:19 pm

Post by Nikki »

Thank you so much, I would never have got that. :)
solimum
Posts: 1420
Joined: Wed May 09, 2007 3:09 pm
Location: Solihull, West Midlands

probabilty

Post by solimum »

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)
Nikki
Posts: 3
Joined: Fri Sep 19, 2008 9:19 pm

Post by Nikki »

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.
SunlampVexesEel
Posts: 1245
Joined: Fri Jul 06, 2007 9:31 pm

Re: Help please - Probability

Post by SunlampVexesEel »

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
Animis opibusque parati
Guest55
Posts: 16254
Joined: Mon Feb 12, 2007 2:21 pm

Post by Guest55 »

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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