PDA

View Full Version : probability question

Tyler
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 /images/graemlins/tongue.gif
09-18-2005, 04:58 PM
Can you figure the chance of none of them having type O blood?
KJL
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
09-18-2005, 05:55 PM
[ QUOTE ]
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 /images/graemlins/tongue.gif

[/ QUOTE ]
FYP

Read this (http://mathforum.org/library/drmath/view/66627.html)
Tyler
09-18-2005, 07:02 PM
[ QUOTE ]
FYP

[/ QUOTE ]
fu

[ QUOTE ]
Read this (http://mathforum.org/library/drmath/view/66627.html)

[/ QUOTE ]

thx
MickeyHoldem
09-18-2005, 07:42 PM
[ QUOTE ]
[ QUOTE ]
FYP

[/ QUOTE ]
fu

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

[ QUOTE ]
[ QUOTE ]
Read this (http://mathforum.org/library/drmath/view/66627.html)

[/ QUOTE ]

thx

[/ QUOTE ]
yw
AaronBrown
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.
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%.

[/ QUOTE ]

Actually it's worse than that - there isn't sufficient information since the population that donates blood is self-selected.
BeerMoney
09-19-2005, 09:25 AM
Where do you go to school?