0

In a list of 20 individuals who volunteered to supply blood, when it is needes for transfusion has 15 individuals of type B blood and 3 individuals are selected randomly from the list, what is the probability that:

a)all three will be type B, b) 2 will be of type B, c)at least 1 will be type B

I am clueless on this one guys so any help or tip will be appreciated!

Chris Gerou
  • 11
  • 1
    Assuming that the people cannot be repeated, the binomial distribution is not super useful here. Chris, what have you tried, where do you get stuck? Is there a similar example that you do understand (this looks like a textbook exercise). – Mees de Vries Nov 09 '17 at 15:39
  • Here is the trouble actually I could use some tip to start, a formula or something! Not the solution cause I am interested in solving it myself but I would appreciate a starting tip! – Chris Gerou Nov 09 '17 at 15:51

1 Answers1

0

a)

Prob that all will be B 15/20 * 14/19 * 13/18

b) the non B can be in 3 positions:

15/20 * 14/19 * 5/18 + 15/20 * 5/19 * 14/18 + 5/20 * 15/19 * 14/18

c) prob that all are not B is 5/20 * 4/19 * 3/18 so prob that 1 is B is 1-( 5/20 * 4/19 * 3/18)

Horseklask
  • 11