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#1 2006-06-18 07:57:02

kcleigh2
Member
Registered: 2005-11-24
Posts: 13

im really rubbish

hi, iv got a few questions tha i really cant get my head around please could someone help me. thanks in advance

Q1) A servey of 3million people in britain found that 25000 of them had a venereal disease.

a) what is the probability of a person in britain having venereal disease.?

The survey also showe that once a person has a veneral disease, there is a 1 in 12 chance thats they will die from it within ten years.

fill in these probabilities, and any others that can bededuced on a tree diagram.CAREFULLY EXPLAIN the meanings of the probabilities at the ends of the branches.

b)what is the probability of a person having a venereal disease and dying from it within the next ten years.?

i am really really really rubbish at maths lol lol lol lol lol lol lol lol lol lol lol lol

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#2 2006-06-18 10:32:14

MathsIsFun
Registered: 2005-01-21
Posts: 7,664

Re: im really rubbish

1A) If 25,000 people out of 3,000,000 have it, that means that 25,000/3,000,000 = 25/3,000 = 1/120 = 0.008333..., so the answer would be "1 in 120, or about 0.0083"

1B) We already know the chance of having it is 1/120, so having it AND dying from it is: (1/120)×(1/12) = (1/1440) = 0.0007 approximately.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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#3 2006-06-18 11:14:28

kcleigh2
Member
Registered: 2005-11-24
Posts: 13

Re: im really rubbish

thanks for that is there anyway that you could help me a litle with the tree diagram i have no idea what this is our tutor did explain it to us but i still didnt get it thanks again

i am really really really rubbish at maths lol lol lol lol lol lol lol lol lol lol lol lol

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#4 2006-06-24 21:47:29

luca-deltodesco
Member
Registered: 2006-05-05
Posts: 1,470

Re: im really rubbish

your first two branches will be

have veneral disease (1/120)
and not have veneral disease (119/120)

from the first branch, you will two more branches
die from it (prob 1/12)  end of branch = 1/1440
not die fro it (prob 11/12) end of branch = 11/1440

from the second branch, well, you dont really need any more branches, so just 119/120, since obviously, youre not going to die from a veneral disease, if you dont have it

and to check, adding it all together

1/1440 + 11/1440 + 119/120 = 1

Last edited by luca-deltodesco (2006-06-24 21:51:39)

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