A bag contains 5 red, 3 green, 12 white and 7 blue marbles. One is drawn at random. With is the probability it is green if it is not red or blue?

Answer 1

This conditional probability
the formula is
P(A│B), read the prob of A given B
= P(A and B)/P(B)

in your case Prob(A) is Prob(green)
B is "not red or blue"

so find Prob(green AND "not red or blue")
and Prob(not red or blue) and sub into the formula

Answer 2

There'sa100 red 50 green and 50 blue beads in a jar what's the probability that I'll pull out a blue bead