Question 798841
Each selected from general population has p(swim) 0.4; p(non) 0.6
a) 
SSNNN
SNSNN
SNNSN
SNNNS
NSSNN
NSNSN
NSNNS
NNSSN
NNSNS
NNNSS
P Each 0.6^3*0.4^2=0.03456
10 ways so x10
p(2swim)=0.3456

b) need Prob not all non-swimmers
= (1-(0.6*0.6*0.6*0.6)) = 0.87