probability question

Tyler · #1 09-18-2005, 03:54 PM

40% of people have type O blood, three random people donate blood. Find the probability that exactly one person has type O blood. This is a HMWK problem for me but the teacher didnt explain how to do it [img]/images/graemlins/tongue.gif[/img]

#2 09-18-2005, 04:58 PM

Can you figure the chance of none of them having type O blood?

KJL · #3 09-18-2005, 05:27 PM

4 out of 10 people have type O blood. So you divide the possible combinations where 1 and exactly 1 person has type O blood divided by all possible ways to choose 3 people from 10. So the calculation is:
C(4,1)*C(6,2)/C(10,3)=50%
Not exactly sure if this is right, but it is my best guess.

MickeyHoldem · #4 09-18-2005, 05:55 PM

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40% of people have type O blood, three random people donate blood. Find the probability that exactly one person has type O blood. This is a HMWK problem for me but I wasn't listening when the teacher explained how to do it [img]/images/graemlins/tongue.gif[/img]

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FYP

Read this

Tyler · #5 09-18-2005, 07:02 PM

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FYP

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fu

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Read this

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thx

MickeyHoldem · #6 09-18-2005, 07:42 PM

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[ QUOTE ]
FYP

[/ QUOTE ]
fu

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All in fun! [img]/images/graemlins/wink.gif[/img]

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Read this

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thx

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yw

AaronBrown · #7 09-18-2005, 08:09 PM

The question is ambiguous. MickeyHoldem pointed to an explanation if there is an infinite population of people. In that case the answer is 3*0.4*0.6^2 = 42.3%. You answered it assuming the population is 10 people in which case the answer is 50%.

If the population size is N, the answer is:

C(0.4*N,1)*C(0.6*N,2)/C(N,3)
= 0.4*N*[0.6*N*(0.6*N-1)/2]/[N*(N-1)*(N-2)/6]
=0.72*N*(0.6*N-1)/[(N-1)*(N-2)]

This goes from a high of 0.6 (N = 5) down to 0.432 as N increases.

#8 09-19-2005, 12:55 AM

[ QUOTE ]
The question is ambiguous. MickeyHoldem pointed to an explanation if there is an infinite population of people. In that case the answer is 3*0.4*0.6^2 = 42.3%. You answered it assuming the population is 10 people in which case the answer is 50%.

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Actually it's worse than that - there isn't sufficient information since the population that donates blood is self-selected.

BeerMoney · #9 09-19-2005, 09:25 AM

Where do you go to school?