finite math
posted by ophelia on .
a box contains 40 computer disks, 5 are defective. Three disks are selected from the box without replacement and regard to order. what is the probability that
a. all three of the disks are defective
b. none of the three disks are defective
c. exactly one of the three disks is defective
d. at least one of the three disks works

d  defective
g good
a) prob(ddd) = (5/40)(4/39)(3/38) = ....
b) prob(ggg) = (35/40)(34/39)(33/38) = ....
c) prob(dgg) + prob(gdg) + prob(ggd) = 3(5/40)(35/39)(34/38) = ...
d) 1  prob(ddd) = 1  (35/40)(34/39)(33/38)