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S1 Probabilty question?? Please help :/

I'm a bit stuck on 6c as when I do the conditional probability formula I seem to get the wrong answer. Any ideas would be of great help. :smile:
(edited 10 years ago)
Reply 1
Original post by ialexxd
I'm a bit stuck on 6c as when I do the conditional probability formula I seem to get the wrong answer. Any ideas would be of great help. :smile:


What answer do you get
89.5%
Reply 2
Original post by TenOfThem
What answer do you get
89.5%

No I get 85% but it is wrong, I believe your answer is right though. How did you do it?
Reply 3
Original post by ialexxd
No I get 85% but it is wrong, I believe your answer is right though. How did you do it?


How did you get 85

I used the conditional probability rule
Reply 4
Original post by TenOfThem
How did you get 85

I used the conditional probability rule


Okay but what was your working out because it says given phone or MP3 player thats what confuses me? Thanks for the help.
Reply 5
Original post by ialexxd
Okay but what was your working out because it says given phone or MP3 player thats what confuses me? Thanks for the help.


Assume 100 people

How many had a phone or a mp3 (or both)
Reply 6
Original post by TenOfThem
Assume 100 people

How many had a phone or a mp3 (or both)


I'm still not sure because assuming what you said it would be 95/100 I think. But when I do the calculation there is something I am doing wrong in the question that makes me get 0.85.
Reply 7
Original post by ialexxd
I'm still not sure because assuming what you said it would be 95/100 I think. But when I do the calculation there is something I am doing wrong in the question that makes me get 0.85.


Why would it be anything other than 95 - that is what the question says it is - can you explain why you are unsure about that
Reply 8
Original post by TenOfThem
Why would it be anything other than 95 - that is what the question says it is - can you explain why you are unsure about that


I mean you said when you worked it out you get 89.5% but I get 85%. When I use the conditional probability formula I get (0.85x0.95)/0.95. What should the calculation be?
Reply 9
Original post by ialexxd
I mean you said when you worked it out you get 89.5% but I get 85%. When I use the conditional probability formula I get (0.85x0.95)/0.95. What should the calculation be?


*sigh*

I am trying to help you understand

Are you now saying that you DO know the number of people with phones/mp3s = 95

Yes or No
Reply 10
Original post by TenOfThem
*sigh*

I am trying to help you understand

Are you now saying that you DO know the number of people with phones/mp3s = 95

Yes or No


Yes sorry I just don't know how to use it to get the answer.
Original post by ialexxd
Yes sorry I just don't know how to use it to get the answer.


jeez - I am trying to help you to get there but possibility 1 is that I just tell you

I prefer possibility 2 where I help you to understand



So

Out of those 95 people how many have a phone
Reply 12
Original post by TenOfThem
jeez - I am trying to help you to get there but possibility 1 is that I just tell you

I prefer possibility 2 where I help you to understand



So

Out of those 95 people how many have a phone


35
Original post by ialexxd
35


May I ask where that came from

The question tells you how many people have a phone
Reply 14
Original post by TenOfThem
May I ask where that came from

The question tells you how many people have a phone


80.75
(edited 10 years ago)
Original post by ialexxd
80.75


May I ask where that does from

The question tells you how many people have a mobile phone
Reply 16
Original post by TenOfThem
May I ask where that does from

The question tells you how many people have a mobile phone


I honestly don't know. 85% have a phone.
Original post by ialexxd
I honestly don't know. 85% have a phone.


85% of what

If you have 100 people - how many have a mobile phone
As the probabilities are given as a percentage, assume there are 100 people.
The question tells you that 5% do not have an MP3 player or a phone.
Therefore 95 people do have an MP3 player or phone.
As this is conditional probability you are finding the probability that the student has a phone, given that it has an MP3 or phone, so you are only considering those 95 people.
Out of those 95 people, you know that 85 have a mobile phone.
Can you work it out from there? Let me know if you need more help :smile:

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