Twenty marbles are in a bag. There are 5 green marbles, 9 blue marbles, and the rest are red. Two marbles are drawn at random without placement. Find the probability that neither is blue

Answer 1

This is the same as both are either red or green.

red = (20-5-9)/20

green = 5/20

Either-or probabilities are found by adding the individual probabilities. This is for one choice.

But you are looking fro two choices. If the events are independent, the probability of both/all events occurring is determined by multiplying the probabilities of the individual events.