Question

A bag contains 4 white beads and one black bead. Three beads are removed from the bag individually being replaced before each selection .find the probability that from the three beads there are at least two black beads

Answer 1

At each draw,
prob(white) = 4/5
prob(black) = 1/5

so you want 2 blacks or 3 blacks
= C(5,2) (1/5)^2 (4/5) + C(5,3) (1/5)^3
= ....

you push the calculator buttons