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Re: The table above represents 100 people grouped by their blood types. [#permalink]
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Bunuel wrote:

The table above represents 100 people grouped by their blood types. The table also shows, for each blood type, the number of people who have a negative Rh factor (Rh-) and the number of people who have a positive Rh factor (Rh+). If 1 person is chosen at random from this group of 100 people, what is the probability that the person chosen has blood type AB or has a negative Rh factor?

A. 0.04
B. 0.19
C. 0.20
D. 0.21
E. 0.99


To answer this question, we can use the classical probability formula:

probability = favorable/total

favorable = #(AB or RH-) = #AB + #RH - #(AB and RH-) =
4 + 17 – 1 = 20

total = 100

probability = 20/100 = 1/5 = 0.2

Answer: C
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Re: The table above represents 100 people grouped by their blood types. [#permalink]
kanishkakarpe wrote:
It is important to note that there's an over lap between the sets. We do have one person with group AB & negative Rh factor.

For Probability(AB) or Probability(-Rh) = P(AB) + P(-Rh) - P(AB & -Rh) =\( \frac{17+ 4 -1}{100 }\) = 0.2

­
Should it not be 0.19? The question asks for a person with group AB OR a negative Rh factor -- So we should exclude P(AB; -Rh) twice, for 0.17+0.4-0.2=0.19

Answer B seems correct (though, of course, Option C is shown as correct)
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Re: The table above represents 100 people grouped by their blood types. [#permalink]
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mattsu wrote:

The table above represents 100 people grouped by their blood types. The table also shows, for each blood type, the number of people who have a negative Rh factor (Rh-) and the number of people who have a positive Rh factor (Rh+). If 1 person is chosen at random from this group of 100 people, what is the probability that the person chosen has blood type AB or has a negative Rh factor?

A. 0.04
B. 0.19
C. 0.20
D. 0.21
E. 0.99
­
Should it not be 0.19? The question asks for a person with group AB OR a negative Rh factor -- So we should exclude P(AB; -Rh) twice, for 0.17+0.4-0.2=0.19

Answer B seems correct (though, of course, Option C is shown as correct)

­
In mathematics, 'or', unless explicitly specified otherwise, means an inclusive 'or', encompassing both condition 1, condition 2, or both conditions. Thus, when referring to individuals with blood type AB or a negative Rh factor, it includes individuals with blood type AB, individuals with a negative Rh factor, or those who have both characteristics. The total number of people having either one or both conditions is 17 + 3 = 20, resulting in a probability of 20/100.

Hope this helps.­
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Re: The table above represents 100 people grouped by their blood types. [#permalink]
mattsu wrote:
kanishkakarpe wrote:
It is important to note that there's an over lap between the sets. We do have one person with group AB & negative Rh factor.

For Probability(AB) or Probability(-Rh) = P(AB) + P(-Rh) - P(AB & -Rh) =\( \frac{17+ 4 -1}{100 }\) = 0.2

­
Should it not be 0.19? The question asks for a person with group AB OR a negative Rh factor -- So we should exclude P(AB; -Rh) twice, for 0.17+0.4-0.2=0.19

Answer B seems correct (though, of course, Option C is shown as correct)

­It should not. In our setup, we account a person who has blood type AB with Rh- in 0.17 once. Then, we account a person who has AB with Rh- again in 0.4. Thus, you should only deduct the repetition count from either one of these group (which is why we minus 0.1 instead of 0.2). 

Deducting 0.2 as you mention means that you are not accounting AB with Rh- in both group, leading to the missing group member. 
­
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The table above represents 100 people grouped by their blood types. [#permalink]
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­Don't forget the one with both:

­
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The table above represents 100 people grouped by their blood types. [#permalink]
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