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Difficult Probability Problem

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Junior | Next Rank: 30 Posts
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Difficult Probability Problem

by jatros123 » Sun Feb 18, 2007 1:44 am
A sample of 1000 persons screened for a certain disease is distributed
according to height and disease status resulting from a clinical exam
as follows:

DISEASE STATUS

None Mild Moderate Severe Totals
|-------|---------|------------|----------|
Tall | 122 | 78 | 139 | 61 | 400
|-------|---------|------------|----------|
HEIGHT Med | 74 | 51 | 90 | 35 | 250
|-------|---------|------------|----------|
Short | 104 | 71 | 121 | 54 | 350
|-------|---------|------------|----------|
300 200 350 150 1000

What would you estimate from the above table to be the probability
of being medium or short in height and having moderate or severe
disease status?

a. 600/1000 * 500/1000 d. 300/600
b. 300/500 e. 800/1000
c. 300/1000
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Junior | Next Rank: 30 Posts
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by jatros123 » Sun Feb 18, 2007 1:45 am
oh..sorry the table got screwed..but i hope u can make sense of it anyways
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The answer is A

by rajorshic » Wed Mar 07, 2007 5:18 am
Add all the Medium height and Short height
Medium height = 250
Short height = 350

Probability of Medium height = 250/1000 as 1000 is the total no. of people
Probability of Short height = 350/1000

Probability of Medium or short is 250/1000 + 350/1000 = 600/1000

Moderate = 350
Severe = 150

Probability of Moderate or Severe is 350/1000 + 150/1000 = 500/1000

Hence ,Probability of Medium or short and Moderate or severe is
600/1000 * 500/1000
Ans: A
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