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# Help with S1 Probability Question?

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1. Help with S1 Probability Question?
An online readers' club has 50 members. Glasses are work by 15 members, 18 are left handed and 21 are female. There are four females who are left handed, three females who wear glasses and five members who wear glasses are are left handed. Only one member wears glasses, is left handed and female.

A member is selected at random. Find the probability that the member wears glasses given that she is left handed and female.

Thanks!
2. Re: Help with S1 Probability Question?
(Original post by Dr.Pwepper)
An online readers' club has 50 members. Glasses are work by 15 members, 18 are left handed and 21 are female. There are four females who are left handed, three females who wear glasses and five members who wear glasses are are left handed. Only one member wears glasses, is left handed and female.

A member is selected at random. Find the probability that the member wears glasses given that she is left handed and female.

Thanks!
Draw a venn diagram.

It is a conditional probability question.
3. Re: Help with S1 Probability Question?
(Original post by raheem94)
Draw a venn diagram.

It is a conditional probability question.
Yeah, done that already. I'm stuck on what to do after that.

I've attached an image of the venn diagram here...

4. Re: Help with S1 Probability Question?
Because there are six sub-categories a Two way table would be easier than a VD
5. Re: Help with S1 Probability Question?
This is how I do it but it might sound a bit confusing ....

You basically look at your venn diagram and tackle the given that part first 'given that she is left handed and female'
and see how many people there are that wear glasses and are female... in your diagram, it's a total of 4.
This becomes the denominator.

Then in this overlap region, you look for the bit where the glasses circle overlaps with female and Left handed or in other words, the number of people who are LF, wear glasses and are female which is 1 here. This part becomes your numerator.

Hope that helps!
Last edited by Jasmine_777; 15-04-2012 at 01:39.
6. Re: Help with S1 Probability Question?
(Original post by Dr.Pwepper)
Yeah, done that already. I'm stuck on what to do after that.

I've attached an image of the venn diagram here...

We have to use conditional probability so we have to concentrate on the region marked in green.

In the region in green, how many members are there in total?
How many member in the green region are left handed, wear glasses and are female?
7. Re: Help with S1 Probability Question?
(Original post by Jasmine_777)
This is how I do it but it might sound a bit confusing ....

You basically look at your venn diagram and tackle the given that part first 'given that she is left handed and female'
and see how many people there are that wear glasses and are female... in your diagram, it's a total of 4.
This becomes the denominator.

Then in this overlap region, you look for the bit where the glasses circle overlaps with female and Left handed or in other words, the number of people who are LF, wear glasses and are female which is 1 here. This part becomes your numerator.

Hope that helps!
You're awesome! Thanks guys

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Last updated: April 15, 2012
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